Why is it defamatory to suspect that Obama is a Socialist...

...when he belonged a Socialist party and spoke at Socialist conferences?

I don't mind people disputing the claim, but I think the attitude that raising the issue is simply ill-manners - like farting in church - is a bit much.

Like the Birther thing, given the fact that Obama promoted, used or was complicit with (a) Socialist politics and (b) the idea that he was born in Kenya, it seems like the burden is on him to overcome the prima facie case he created.