"Stating an opinion" is basically asking for feedback, whenever positive or negative. You don't "state an opinion" for the sake of it, there is an underlying intention behind this seemingly innocent practice. The reasons are usually:
-Generate controversy, something easily confused to what is called trolling if lacking in subtlety
-Become justified in your own beliefs by community agreement
-To convince people of something, depending on the wording it may become a very annoying example of "pushing your beliefs upon others"
Basically, you have no reason to do this other than trolling.