There's a difference between voicing a contradictory opinion, giving out bad advice, and deliberately phrasing something to start a fight. For example:
"I've never cycled a tank and all my fish are fine." Well, if you don't count introducing a large bacterial population by pulling media from an established tank as cycling, this can be true. By not stating the means of establishing bacterial colonies, this statement can cause some serious problems. If you say "I prefer to use media from an existing tank instead of cycling with fish or fishlessly", no one will blink an eye.
Or:
"I don't think it hurts goldfish to be kept in a 5 gallon bowl." Well, for a few minutes? For life? This is a statement that is going to upset someone. Sure, there are many that think it's fine. Just like "It doesn't bother me to replace all my fish every 6 months-they're all cheap, anyway." People are entitled to their opinions, but some attitudes are not welcome here, and some opinions are offered as fact, when they are clearly not.
And, of course, any number of inflammatory statements could be offered up. Some trolls just hit and go, satisfied that they've started a fight.