Sometimes they are, but I think this was always the case in one way or another. Original thought has always been the province of a lonely few, irrespective of politics. "Groupthink" sounds like an evil, Orwellian hell, but actually it is the norm for many, many people in all kinds of professional pursuits.
It takes real intellectual discipline to avoid falling into the trap of familiar, generally accepted patterns of thought. One problem in today's humanities universe is undoubtedly comfortable multiculturalism; in an earlier era, problems were comfortable canon-worship, or comfortable scholasticism. I think there is more diversity of opinion (and specifically, more political and cultural conservatism) in academia than most people think. But I also think the overall intellectual climate -- the openness of thought, the willingness to engage with people who hold differing opinions -- could be a lot better than it is.
Still, Mark Bauerlein thinks it's a serious problem, and makes the case in an essay in The Chronicle. Erin O'Connor agrees with him.
I posted a comment on her site disagreeing on tone, not so much on substance.