I think Wikipedia should develop some very clear rules about users contacting, harassing and bullying other users. Spamming and stalking of fellow users should likewise be frowned upon.
If Wikipedia's user base is large enough that it is basically a social network in addition to being an online encyclopedia then the same privacy rules used in a social network need to be observed.
The ability to send email to other users should be removed. Want to send a message? Leave it on the person's discussion page. Allowing people to covertly contact, stalk and harass a person only serves to give Wikipedia a bad reputation.