The difference is stating something as a fact "x is dumb" and stating something as opinion and using it as opening to talk about it with others "I think x is dumb and here's why, let's talk about it".
X is not dumb just because you think it's dumb. Is there any real point to the thread or is it just you ranting about something you personally dislike? When you state something like that it should be as a basis for a discussion since this is a forum, not your personal blog, and as such it should be somewhat objective or openly stated to be your personal opinion instead of trying to hide it as a fact.
Additionally stating something like "x is dumb" as a fact about something you know several people enjoy without formulating it in a way that invites others to a friendly discussion about it, comes over as somewhat combative. I don't go into the Chaos forum and open a thread just to say "Chaos is dumb" either and there would really only be two reactions I could expect from such an approach ... either people being defensive because it was to be expected they disagree with me or people saying it's subjective in an attempt to smooth out the clumsy approach of the OP (me).
You are perplexed by people stating that it's subjective ... I'm perplexed that I have to explain to you how interaction on a forum works. In germany we have the saying "Der Ton macht die Musik." which basically means "It's not what you say, but how you say it."