Okay, here is the honest truth about your 'negative' opinion on a champion:
No one cares what you think.
X is a bad jungler.
X isn't a good support.
X can't top well.
X is only good in certain teams.
X isn't played by professional players in tournament.
X has no presence as a jungler.
X is weak to invades.
X has no sustain.
I can't count the number of times someone was enjoying the game, dominating as a champion, watching a gimmick play out, or just doing what they wanted to do... only to have some complete toolbag start pointing out the drawbacks.
It's a game. If you can't enjoy it, fine, but stop trying to rain on everyone else's parade. You think anyone carrying a game wants to hear that they are only gettting lucky, or they could have been counterpicked? No, they'd rather you congratulate them on wrecking face.
Even worse on the forums. One example: Support Nidalee is bad blah blah. She has no poke or late game blah blah. Look at my match history. I had fun. I did well. I won. I don't give a flying fark what you think about it's flaws dipstick.