Or they want knowledge of the hoax to spread, so as to protect the victim against further lies?

Just because you don't consciously believe something to be true, doesn't mean you don't care about its veracity. The null hypothesis is that people are willing to treat things as true based on their priors — which could be informed by things as simple as "this was posted on a website not known as a den of misinformation, and shared on HN" — while not actually devoting thought to an investigation of the truth.

Or not engaging enough to come to any conclusion - just chuckle - upvote. Useful, but not idiots nor villains

If your goal is to burn down tesla/musk, you logically promote everything remotely damaging.

And there are plenty rational reasons to have that goal.