I need to qualify my "I don't care if there are quadrillionaires" comment.
In theory, all other things aside, it is true. I mean, look up at the stars. For all I know there are functionally immortal super-minds out there who have not known pain for millions of years. Their existence is not a problem for me.
But "we live in a society," and unfortunately other peoples' extreme wealth can cause problems for me.
One is by bidding up assets. The super-rich park their money. Parked money goes into things like PE. PE can't find enough stuff to do with it, so they do shit like buy up housing and hold it off the market to profit from real estate appreciation. That makes it harder for me to find a good place to live. That's just one example.
I actually coined a term for the above: financial pollution. Financial pollution is any time someone else's money being invested does harm rather than helps, usually by driving up asset prices, massively distorting a market, or being invested in the creation of rent-seeking schemes. A classic example of financial pollution would be the real estate market in cities that allow a lot of overseas investors to park money in real estate.
Financial pollution is the opposite of productive investment that does things like creates jobs and builds things.
Another is that extreme wealth distorts politics. One of the libertarian things I like in theory is the idea of separation of economy and state, but in practice that's a brutally hard thing to achieve... much harder than separation of church and state. It is true from a social contract and legal point of view that money is not the same as physical coercion, and the state has a monopoly on the latter, but if you have loads of money you can buy the people who run the state and therefore obtain direct access to physical coercion. That's the problem. The super-rich can buy the government and then use force to maintain their status or pursue their own personal cultural, religious, or national peeves and hobby horses.