I don't even think they're hating on "social VR" as a concept, so much as they are on
the specific involvement of Facebook.Facebook has accumulated enough ill will over the years -- with its cavalier attitude towards users' privacy, with the multiple times it's screwed over developers who bet the farm on their platform, and so forth -- that people just automatically assume now that if you lie down with Facebook you get up with fleas. "Facebook" means technology that, at its heart, is looking for a way to screw you over. It's a tainted brand.
If it were any other company making this acquisition -- Yahoo, Google, Microsoft, anybody -- you'd see much more willingness to give it the benefit of the doubt. But people see the Facebook logo being slapped on the Rift and assume, from bitter experience, that this means their Rifts will be turned against them, in the same way that Facebook turned their browser and their smartphone and their network of friends against them.