Firstly, there's the myth of a "free trade" - that requires both parties to have sufficient knowledge about the deal/product and to have equal bargaining power. That's a very rare thing with Capitalism as the richer party will have much better access to information (and also the influence to bury certain information) and will have a much better bargaining position in any negotiation.
Secondly - even though two parties trading with each other can both obtain an advantage from the deal, that's often at the expense of parties not involved with the deal e.g. I can go and buy cheap groceries at a discount supermarket, and would consider that both the supermarket and I benefit, but that will often be at the expense (or due to the exploitation) of the food producers and workers.
> You sound like a communist.
Thank you, but maybe "socialist" is a more acceptable political term
You can’t freely consent if someone has power over you, and in a Capitalist system Capital has power over labor. Capitalism is therefore abusive and exploitative, by design.
For the record, I am not, nor have I ever been, a Communist.
> Therefore, having a billion dollars is a clear sign that millions of people have been exploited by that billionaire.
When two people enter a trade freely, they both come out richer. How is that at the expense of other people?
You sound like a communist.