Almost every problem in the world would be dealt with meaningfully if we outlawed billionaires.
Everytime I look at small problems or big global problems, if you follow the money trail, it all leads to some billionaire who is either working towards increasing their wealth or protecting their wealth from decreasing.
Everything from politics, climate change, workers rights, democratic government, technology, land rights, human rights can all be rendered down to people fighting another group of people who defend the rights of a billionaire to keep their wealth or to expand their control.
If humanity got rid of or outlawed the notion of any one individual owning far too much money than they could ever possibly spend in a lifetime, we could free up so much wealth and energy to do other things like save ourselves from climate change.
Wealth is just one means of power. Destroying all billionaires, while a good step, would not even come close to solving almost every problem in the world.
Right now billionaires are a huge bottleneck to global development and those people who actually want to do something about our worlds problems. Getting rid of them won't solve our world's problems ... it will just make our problems easier to solve. Leaving them alone means our problems persist while they actively block everyone else from dealing with the world's problems.
Throughout history power has been used to obtain wealth and comfort. So if you remove the ability to leverage power for wealth, you remove the primary motivator for obtaining power for most people. There are certainly people who want power for the sake of power, but most people want power to obtain comfort.