I personally don't believe it's 50/50 - I think it's the common case of a very vocal minority. People who have issues with things, whatever it is, are more likely to come out and express their concern. Whereas, when the fast pass plus system goes right, it's the kind of thing you might not even notice on your trip, and those that have positive experiences with it I likely won't say anything at all on forums such as these.
I could be 100% wrong, though! And either way, I'm not trying to take away from people who have expressed their opinion or bad experiences. I'm just saying angry people are louder than content people.