I don't think most people are selfish to the point of it being harmful. I think the problem is that a small number of people are, and those are the people who are in charge of things, where their selfishness can do way more harm.
As others have mentioned, though, a lot of behavior is heavily influenced by the incentive structures people live within. This can apply in very obvious ways: for example, when trying to get from point A to point B, people will use the mode of transportation that makes the most sense for that trip, which is heavily dependent on the infrastructure that exists between those two places, and that's why the Dutch will bike five miles, the Spanish will catch a train across the whole country, and people in Houston will drive across the street. It can also apply in more subtle ways, though, and that's where capitalism comes in. To pick one example, companies that are owned by their workers are more stable and better places to work than traditional privately owned or shareholder-owned companies, but it goes far deeper and gets far more complex than that, too.
People are responsive to economic incentives. If the incentives favor doing good things, then good things happen. Otherwise, you get what we have now.
Then humanity is fucked.
Oh, boo hoo, won't someone think of the poor rich people, having to pay extra to keep their disgusting riches safe from the people they fucked over to get them. I'm sorry, I've been trying not to contribute to the toxicity I see in these threads, but come the fuck on.
Besides, I don't think people envy the rich and powerful the way you're describing, I think people envy the idea of being able to maintain a good standard of living without having to work themselves to the bone to do it, and they begrudge rich people's wealth and power on the grounds that they use it to influence politics and deny a decent standard of living to the working class. I don't want a mansion and fifty nice cars, I want an apartment in the city in walking distance to transit and stuff to do, and then to also save more money at the end of the month than I did at the start. Most people are similar: their specifics might be different, but the broad strokes are the same, especially the last bit.