Because you don't generally get to DECIDE to be a baron? You can inherit one, in which case a psychopath can to a large extent do what he wants with it without suffering repercussions, you can be granted one by the king (which is at least SOME sort of incentive system), or you can get a bunch of random guys together, start and army, and take one. At which point you can usually do whatever you want with it.
Of course rich guys can do a lot with the power they have once they have it, but the path to getting it is far more likely to involve helping a lot of people if it needs you to convince a bunch of different people to give you money for your services.
The original question was why would sociopaths bind themselves by the rules of capitalism, but not by rules of other socioeconomic systems. That's a different question than whether sociopaths' climb to the top can be made useful for others.
This thread is for asking any questions that might seem obvious, tangential, silly or what-have-you. Don't be shy, everyone has holes in their knowledge, though the fewer and the smaller we can make them, the better.
Please be respectful of other people's admitting ignorance and don't mock them for it, as they're doing a noble thing.
To any future monthly posters of SQ threads, please remember to add the "stupid_questions" tag.