I think I get why people don't like the GPL -- it forces them to do something, whereas other licenses don't. If you use GPL'd code, your code has to be GPL, there is no option. If you use BSD code, you have the option of making your code free, or you have the option of not doing that.

I read a book called "Predictably Irrational" that documents this effect. The author set people up with a computer game where the goal was to run around and collect as many points as possible. Bags would randomly appear, you would collect them, and that would get you the points. Different rooms had different rates of points appearing, and some rooms would produce higher value objects, etc. He tried a variety of scenarios to see how people would behave; one involved a door to another room (which might have more earning potential than the current room) that you could travel through at the cost of a certain number of points. If you didn't go through the door, it would eventually disappear. He found that people, even after finding that the room that the door led to was worthless, would still waste time and points to keep the door open. Nobody wanted to let an opportunity, even a poor one, pass.

I think this explains the (predictably) irrational hatred for the GPL; it makes doors close, and that is something we are apparently hard-wired to hate. Even though we know we are never going to make our free app proprietary, we want that option.