I don't think it's the most common case. Most common is when you find something obnoxious about a post. But it's common enough and (as pg has said several times

I don't think it's the most common case. Most common is when you find something obnoxious about a post. But it's common enough and (as pg has said several times) legitimate enough that the people (not you!) who indignantly protest "That's not what downvoting is FOR!!" really have no basis for doing so. A certain amount of groupthink is probably inevitable in a community, but is there evidence of it being a big problem here? For example, are there many (any?) heavily downvoted comments that don't fairly obviously deserve it? People call "groupthink" sometimes when they don't want to see how they were being rude. A far worse problem in my view is the huge area under the curve at the tepid mean. It's hard to downvote a comment just for being bland and pointless. It would be nice if HN could solve the problem God solves in the Book of Revelation: "So then because thou art lukewarm, and neither cold nor hot, I will spew thee out of my mouth."