I think I'd probably qualify that, we are partly selfish and therefore democratic capitalism suits us the best.

Pure socialism doesn't work, because it relies on everyone being totally selfless. But they aren't, so the system is very easy to exploit.
Pure capitalism in practice would be almost indistinguishable from pure socialism in practice... winner becomes fabulously wealthy, majority of the population are so poor that they struggle to survive.

What makes things work is democracy (however imperfect it may be). This is because it provides an essential counterweight against extremist ideology. People often disagree quite vehemently about how governments should behave, and the extent to which they should work for the populace against the extent to which they should enable businesses to flourish... but it's generally simply a question of degree. Most people would agree that any system that lacks a counterweight would be a terrible idea, and cause a lot of suffering.