Capitalism is explicitly designed for people to benefit themselves at the expense of others. Capital begets more capital in a positive feedback loop that results in massively powerful billionaires.

If you elect representatives, those representatives are checked somewhat by the threat of being voted out. Capitalism has no such check. Sure, ostensibly people can choose not to buy a product, but unregulated capitalism selects for monopolies.

And now we find ourselves at the beginning of the meme.

Also, I find "people are greedy" to be an uncompelling reason to support a system that incentivizes greed and exploitation. If people bending a system to benefit themselves is a problem, then the system should be designed to be resistant to this, in a way that incentivizes promoting the common good. Or at the very least shouldn't encourage these problems.

Capitalism encourages these problems.