Last time I checked, billionaires still need to follow the law, so yes there is most definitely checks for them. If you don't like something they're doing, ask your representative to outlaw it, if you can't lobby for a law against whatever they're doing, it means unlike you, your fellow citizens don't think their actions are bad, so it's completely fair.I think the issue with these mega rich billionaires is not so much that they are totally good or totally evil - all of us humans have good sides and bad sides. We can all be selfish, selfless, whatever, we can all make silly mistakes or say silly things, and we all have capacity to do great good. The problem is when one person ends up with untold billions of dollars, all of these things are amplified massively, and affect tens of thousands of people. In democratic countries we see the need for checks, term limits and scrutiny for our elected officials, as power has a corrupting effect. Billionaires like Musk don't have these checks, so bad things, as well as good, can happen.
I guess what I'm saying is it's not good for so much wealth to be in one man's hands.
And government wield so much more power than billionaires, for example the US federal government spent $6.8 trillion last year, about 30 times of Elon Musk's entire net worth, and that's just the government spending for a single year. And let's not forget government is the only entity who can legally use violence, including the power to wipe humanity off this planet, so yeah having more checks on government is more than justified.