I think that raising the sanity waterline is a worthwhile goal, but picking your battles is absolutely necessary. It doesn't matter how formidable your argument is if you're arguing in the comments of a youtube video, you've lost by default. So where is the line in the  sand? Where would you feel compelled to take action, and to what lengths would you go to? What price would you be willing to pay?

I'm a psychology student, third year and currently doing a unit called "cultural psychology". The lecturer has advanced notions of "multiple truths" and how "reality is socially constructed". To quote him directly in regards to this:

"There is a tendency for those who believe in one reality to use the physical world as a basis for argument, while those who believe in multiple realities use the social world. Even in physics we have 'reality' changing as you get closer to the speed of light, and the laws of physics don't apply prior to the big bang. These are fairly extreme situations. In this course we are dealing with social realities and the point is that different cultures operate in worlds that can be quite different. To see this purely as a perspective risks the dominant social grouping seeing their reality as the true reality, and others as having a different perspective on that reality. The assumption that cultures can have different realities places every on a level playing field with a dominant culture calling all the shots."

You can see in the last line the conclusion he wants his premises to support. The exercise is not to pick his argument apart, find all the holes and write a crushing riposte (although you can if you're so inclined).

The question is, if the goal is to raise the sanity waterline, is this a battle worth picking?