It's simply not worth the effort. Forget about the political topics you mention for a second. Changing minds in that realm through conversation is know to be hard. Look at something easier like conveying factual information about non-controversial topics.

Even in that case, if a topic is complicated enough that an early 20's newbie can't pick it up from a 1000-word medium essay, forget it. People who engage in trying to inform are fighting a constant uphill battle with no upside if they succeed.

Now pile the baggage back on of trying to disagree the "conventional wisdom" of a social bubble. A few try, most give up, and the spiteful join the jokers in trolling.

If you care about your karma level, you have to be careful about it. There are some perfectly reasonable positions that attract downvotes from some quarters. At the end of the day, it's just internet points, though. Sometimes unpopular things need to be said, if for no other reason than to register the existence of dissenting opinions.