Do people hate Outbrain because Outbrain does this? Or is it due to the nature of their ads? (I'm assuming we're talking about the "Around the Web" chum boxes, right?)

Yep the hate is probably for the type of machine generated click bait content that ends up on there. But other than that they do advertising right. Each ad is a picture, some text and a link. All hosted by Outbrain.