shakespeare's words become more intelligible : nothing is either good or bad, but our thinking makes it so.
It's not just our thinking alone, but also how someone who wishes to say something unpopular or controversial chooses to do it. It's a lot in how you say it.
Bladeforums, not surprisingly, is a fairly pro-knife group. If a person came here wanting to advocate for the illegalization of knives, that would be an unpopular position. But would that fact necessarily make that person a troll? No.
If that person said, "You are all filth, stupid idiots for liking knives. And all knives should be illegal." then yes, that person would be on his way to trolldom.
And if someone asked politely, "But how would we do life-saving surgery withou knives?" and the OP refused to consider that argument, then he would move closer to the troll title.
Whether or not a poster is a troll does depend on what the group as a whole thinks, yes. But it also depends on how that person states his ideas and opinions, how he acts, and really what his apparent purpose and goal are.
In the hypothetical case of the person on bf.c advocating the illegalization of knives, I suspect that there would be 100% chance of a troll in that thread... but I give 50/50 as to whether it would be the OP or one of us. You can be a troll advocating the popular opinion too.