As for ‘betrayal’: although it has been overused, I believe this notion is sometimes apt, in political as in personal affairs. People can betray comrades or supporters; or their own stated principles. I think an excellent example of the latter case to be, precisely, the conduct of many ‘anti-militarist’ social-democratic leaders at the outbreak of the First World War...
Norman Geras, 1988.
I am not going to pass any kind of extended comment on Norman Geras, who I never knew personally, and who passed away yesterday, other than to say that he was once a Marxist - indeed a Trotskyist - who wrote some important work on matters including Rosa Luxemburg and human nature before betraying his comrades and own stated principles by cheerleading Western imperialism in a vocal manner on the blogosphere for the last decade or so of his life while trying to keep up the pretence he was still somehow on the 'Left'. One of his best and most important books was entitled Literature of Revolution - his blog in contrast might best be filed under 'Literature of Imperialism' - and so is destined to be ultimately confined (to borrow a phrase from Leon Trotsky) to the 'dustbin of history'.
Edited to add: Obituary in Socialist Review by Paul Blackledge