Q: Why is social democracy labelled socialist or within socialism?
A: Because social democracy is not all welfare states, which have been supported across the political spectrum by some types of conservatives, liberals and socialists.[nb 1] Social democracy is one of the many traditions within the socialist movement. In addition, the most common name for the classification to which social-democratic parties belong to is socialist. These parties were mostly associated with the Socialist International. Many of them self-describe as democratic socialist or social-democratic. When we use these terms to describe parties, etymologically they mean the same thing. We do not want to imply that they have two ideologies under the same roof as, for example, the Democratic Party does with Bernie Sanders, AOC and Ilhan Omar as "democratic socialists" (which is what they call themselves) or social democrats and all other major leaders as liberals. Of course, socialist parties have left–right divisions and they are sometimes called democratic socialist and social-democratic. The new party family that has emerged, which is broadly made up of Marxist–Leninists, Trotskyists and more left-wing socialists, is now generally referred to as "left parties".
Q: Still, why is social democracy considered socialist?
A: While social democrats have not turned capitalist economies into socialist ones[nb 2] for pragmatic reasons, among others, socialism is not only an economic system but a political philosophy, too. First, socialism can mean either an ideology or an economic system, while capitalism is mainly simply defined as an economic system. Under classical Marxism, socialism is a stage of the economy that would replace capitalism and was the name that Communists used to describe the economic systems they implemented. As the definitive Historical Dictionary of Socialism points out, socialists disagree about the degree to which regulation of the economy is necessary; how far society should intervene and whether government, particularly existing government, is the correct vehicle for change are issues of disagreement. And they are anti-capitalist only so far as "there were general criticisms about the social effects of the private ownership and control of capital—poverty, low wages, unemployment, economic and social inequality, and a lack of economic security." In addition, party ideologies are generally static, although policies change over time. As an example, the Tories have changed their policies since the days of the English Civil War more than Labour has over its 120 year history, yet are still considered conservatives.[nb 3]
Q: But social-democratic parties are not socialist and do not identify with socialism, do they?
A: That is not true, most include mentions of socialism in their party constitutions, describe themselves as socialists and are routinely called as such, being categorised by academics as part of the socialist party family. The philosophy of social-democratic parties such as the Swedish Social Democrats was that if people were healthy, well-educated and had a decent standard of living, that they would seek to develop a socialist society. They did not consider the welfare state to be socialism but a necessary condition for its development. However, as the Swedish Social Democrats built the most comprehensive welfare state, the welfare state is sometimes referred to as social democracy. Of course, socialism/social democracy as the Social Semocrats understood it did not happen and right-wing parties in countries such as Sweden, among others, also came to support the welfare state. The SPD describes democratic socialism as its ideal, with social democracy serving as the "principle of action". Some socialist parties use that to mean a post-capitalist order while others use it more in a utopian and idealised sense to describe an egalitarian society, where features such as discrimination and poverty are eradicated, which would still be starkly different from current capitalist society to be considered a post-capitalist one. Both of these are perfectly in line with the definition given by the Historical Dictionary of Socialism and it is more of a spectrum than a hard line.
Q: What is the difference between, say, Corbynism and Blairism? Surely the difference is that the first is socialist and the second is liberal?
A: Not so easy. The difference between Corbynites and Blairites, or the difference between the left and right wings within socialist/social-democratic parties, is not that the former are socialists and the latter are not, but that they have different conceptions of socialism. Admittedly, many people question whether any of them are actually socialists. Yes, those to their left accuse those to their right within the party to not be socialists; yet, those to the left of both accuse them of not being socialists but reformists.
Appendix

Socialism and socialist are loaded terms in the United States and right-wing media while in the rest of the world they are usually just one of two major parties. When describing foreign leaders, American media only uses the S-word for socialists they oppose and never use it for those they support. So Maduro is routinely referred to as a socialist while Guaidó, a former member of the socialist/social-democratic party Popular Will (still affiliated to the Socialist International and described as social-democratic, "with socialist and progressive tendencies"; note that it is the Maduro government that says Popular Will is "fascist" or "right-wing") never is. Being opposed to Chavismo, or Madurismo, does not necessarely mean being opposed to socialism; there are at least as many types of socialism as there are months in a year.

In addition, "[m]ost critics cite anti-democratic governance, corruption and mismanagement of the economy as causes of the crisis" rather than socialism[nb 4] and even those who blame policies for the crisis, only a few say "socialist policies" and they mostly say "populist" or "hyper-populist" policies, which are not the same thing. This should not stop us from following academic sources that use socialism, in a neutral manner as provided by the Historical Dictionary of Socialism, to refer to social democracy.

Footnotes
  1. ^ Social democrats continue to fit within the definition of socialism provided by the Historical Dictionary of Socialism, pp. 1–3. The different groups will differ in policy based on ideology, even when the policies appear similar. As an example, liberals, conservatives and socialists created welfare programs in the United States, Germany and Sweden, respectively, but for different reasons and implemented them differently.
  2. ^ If you use socialist economy to mean the Soviet model, of course they have not turned capitalist economies into socialist ones; yet, they moved them closer to socialist ideals (Jerry Mander describes the mixed economy as "an active collaboration of capitalist and socialist visions"), so much so that social-democrat Anthony Crosland argued that "traditional capitalism has been reformed and modified almost out of existence, and it is with a quite different form of society that socialists must now concern themselves. Pre-war anti-capitalism will give us very little help", for a new kind of capitalism required a new kind of socialism. Of course, "Crosland believed that these features of a reformed managerial capitalism were irreversible, but it has been argued within the Labour Party and by others that Margaret Thatcher and Ronald Reagan brought about its reversal in the 1970s and 1980s. While the post-war consensus represented a period where social democracy was 'most buoyant', it has been argued that 'post-war social democracy had been altogether too confident in its analysis' because 'gains which were thought to be permanent turned out to be conditional and as the reservoir of capitalist growth showed signs of drying up.'" Still, many legitimate academics, economists and scholars have disputed the Soviet model as socialist, calling it centralised-managed (rather than planned; and planning itself, which has been adopted by many capitalist and non-capitalist countries, or a planned economy is not necessarely socialist), command economy, state capitalism, or another non-socialist mode of production; so socialist economy cannot be reduced to that.

    It is not original research to discuss whether social democracy as used to describe the Nordic model developed by the Swedish Social Democrats and social democracy as used to describe the ideology of the party are the same thing. The same applies to the Soviet Union. While their system is frequently referred to as socialism, only anti-communists and Marxist–Leninists consider it to be so in reality. The issue is whether or not the economy was in the control of the Soviet working class and whether the Communist Party of the Soviet Union represented them in a democratic way. And the same applies to Bismark's State Socialism or to reference any other capitalist society as socialist.
  3. ^ Liberals no longer insist that government spending be under 10% of GDP, while conservatives no longer insist that hereditary peers have equal or greater power than elected MPs.
  4. ^ According to Asa Cusack, an expert on Latin America and frequent contributor to mainstream media, Venezuela's economy remained "market-based and private-sector dominated" throughout Chávez's time in office. Although "the social economy and the public sector were heavily promoted", for example through nationalisation, "the private sector was expected to remain dominant, and it did. A centrally planned socialist economy like Cuba's was neither the aim nor the reality." Even Fox News, before things went bad and socialism became the boogeyman, reported in 2009 that roughly 70% of Venezuela's gross domestic product was created by the private sector; so during the 2000s economic boom, Venezuela was still capitalist (good) but as soon as the 2010s economic crisis hit, it became socialist (bad).