Probably the fact that many of the anti-4e posters --
-- use perjorative and condescending concepts such as "4e is dumbed down" and "4e is for little kids" (thus basically stating that anyone who likes it is a moron whose opinion can be discounted).
-- complain endlessly about EVERYTHING. NOTHING about the new edition can be done right. It's all wrong, wrong, wrong, the people who make it really hate D&D and are showing disrespect for Gary Gygax and Arneson and everybody else up to and including the Holy Roman Emperor.
-- declare the absolute perfection of everything except 4e. If it's so perfect, why does it bother you that 4e is coming out? Go play the edition of your choice. It's no skin off your nose if somebody else plays a different edition. Your favorite edition exists.
-- positive comments are invariably dismissed flippantly as "fanboyism," "ignorance," "condescension," and "extremist views," while everything that is negative about 4e is lauded reverently as "finally, something balanced," "impartial," "rational."
I've seen far, far more of these posts than anything resembling 'rational' and 'respectful' analysis.