The important question is what you're trying to define. Are you trying to define existing system or some your ideal?
If you're trying to define existing system, I would disagree that exchange is voluntary here, unless you play with words and say people are free to die of hunger. (Also it's not clear what "private ownership of labor" means.)
If you're as capitalism designating some other ideal system (based on your values), for example anarchocapitalism, you should be aware that these always failed too, sometimes even more horribly than attempts for communism. But then anyway, why would you attempt to call this ideal "capitalism"?
This is actually the basic contradiction in your thinking. You say "the system we have is not really a capitalism", so the problems (that many people see) are not problems of capitalism. But then why do you want to call it capitalism, if not as the reference to what we have today?
