The rootkit thing was one major reason. There's also the Lik-Sang incident, the PS3 OtherOS nonsense, BD+ and the mandatory encryption on Blu-ray discs (your home video footage of your kids certainly needs DRM, right?), phony movie reviewers, exploding laptop batteries, huge breaches of personal data including credit card numbers that they try to sweep under the rug, and all the little things they do all the time, like how practically every model of every one of their products has a new, incompatible, proprietary standard USB connector and memory card format.* Basically, it's because they're huge jerks that screw over their customers much too frequently for my liking.
Of course it's difficult to avoid ever buying anything they make, since they make all sorts of tiny components, but I do my best. I don't buy a lot of media/electronics to begin with, so it's easier than you might think. None of your list, for example.
Do you vote? You realize that whenever you do business with any corporation, there's a decent chance that money is going to support one of the other candidates? And that one vote is a drop in the bucket? But you do it anyway, because you have your vote and you don't want to waste it. And if enough people do that, what do you know, it starts to make a difference. Same scenario. Vote with your wallet, as they say. Maybe Sony won't notice my actions as an individual, but that doesn't mean I'm just going to ignore all their wrongdoings and keep giving them my money. And of course, I try to
educate others as well. Read over that article and the sub-pages linked from it and tell me you're not at least a bit irked.
(*yes, this is an exaggeration, but just barely. Look at PSP. New model? New cables! New PSP?
New memory card format! And "Universal" Media Disc, that only works with certain models of one device...)