Any political or quasi-political debate must begin with a defining of terms, so that when people use the same words they mean the same things by them. If we permit "Capitalism" to be defined as "The economic system that lets me and those like me make as much money as we can" and "Socialism" as "anything that gets in the way of that" we have problems.
Under "pure" capitalism, the big fish eat the little fish until there are no little fish left and one entity ends up running everything, the government included. Good for them, not so much so for everybody else.
I favor a system that I've come to call "socially-responsible capitalism", which is not
socialism any more than the "socialism with a human face" advocated by Dubcek in 1968 Checkoslovakia was capitalism. It was, however, enough of a threat to the Stalinists in Moscow for them to send in the troops.
"Capitalism" has it's Stalinists as well, they're just a little more subtle.