The same reason Apple bothers me.

Today, I don't care. His clients know what they're getting involved with, and if they don't care, I don't either.

My concern is when he does go to Mars, he'll have hundreds of people signing up not realizing that he's putting lives on a beta rocket.

Oh, he clearly stated that lives would be at risk for the first flights. I can only imagine the contracts you have to sign, when signing up. If those people do not read them, you cannot blame Musk.

He's very upfront about the risks to the first visitors/colonists. His first screening questions for applicants is literally "Are you prepared to die?"

Popular false beliefs always seem harmless until they suddenly aren't. The principle of explosion means that one false belief can justify literally any course of action, and by the time people start on a harmful course it's too late.

For the principle of explosion to work you have to actually confirm that a belief is false, or at least calculate a justifiable probability that it is false. You can't just assume that it is false and extrapolate from there.

The point is you can't assume it doesn't matter because it seems harmless-if-false. The grandparent asked "why do you care [whether the things Musk is saying are true]?", but the answer is that you have to care about anything that's likely to influence a large number of people.