I don't think most of them would even view it as "wiping out most of humanity". Like much of the past, it is simply a complete ignorance of the circumstances of the lower classes. They have everything, and they assume that everyone else that is worthy has what they need too, just like they do. They are oblivious to the suffering that their selfishness has wrought. They might even believe that it is an inevitable tragedy. So don't get me wrong, I don't believe these ultrawealthy are necessarily "eradicate humanity" evil. It is just that their desired world will come at the cost of everyone else.

As for what I would do if I inherited Elon Musk's wealth tomorrow: I would do exactly what any ultrawealthy person would do, and use the interest to live and accumulate more interest. I would very much like to engage in philanthropy and speak my views to those who would listen (but having money does not make me a better communicator). I could donate to political parties I align with. But I do not have the same drive for accumulating more assets (indeed, I would actively avoid this), so I would become progressively less wealthy than my ultrawealthy "peers" until I am only wealthy and not ultrawealthy. I would still live extremely comfortably until I die. But unless I can convince the rest of the public to fight back against those few that probably do wish to eradicate/control much of humanity through technology and asset accumulation, nothing will change.