If someone can back their opinion up, and tell people why they feel how hey feel, I see no reason why people should be mean about that. However, If you say something hurtful or inappropriate just for the sake of starting a sh*t storm and call it your "opinion" then you shouldn't be surprised when people tell you to f*ck off, or shut up and keep it to yourself. All in all, if your opinion is informative and useful in any way, or you have a way to back it up, go ahead and say it! But if you are just talking to hear yourself talk, then stop.