There is no argument. People spend money on what they want to. Maybe he has some interesting reason for it or maybe he just believes it to be a good investment.

I'd like to think Musk has a plan for Twitter to be his Washington Post but people aren't even that rational so who knows.

Hopefully, he's ignoring the SEC again and trying to make money by saying random and dodgy things to make money. Or, just trying to show how clever he is and how his actions are unrestricted.