Part of the reason it gets the sneering that it does is because a lot of the first people to leave LJ for DW were slashfic writers who were worried about LJ shutting down their communities.

I seem to remember that it was spearheaded by Potterverse 'ficcers because LJ was cracking down on depictions of underage sex. DW swore they'd never do that, so for a while they had a reputation of "Bring me your pervy, your kinky, your outrageous anti-canonical pairings yearning to breathe heavy..."

Every time there's LJ drama, a few people announce That's It, I'm Going To Dreamwidth.