Revolution and the end of capitalism aside, I have yet to find a Lib who can explain to me why it would be wrong to take everything from the rich except, say, 500 million. There would be no losers. The rich would still be rich, but we could do so much good with the money.
Theft is what happens every day in every working relationship. Value is always and exclusively derived from labor. If someone has capital worth 500 million, that means they have the labor value of 500 million. Did they earn this value themselves? Of course not, it is the value of our labor that they have stolen.
But even if that weren’t the case, this argument is roughly on the same level as “drugs are illegal because they are prohibited.” Always remember: in the Third Reich, it was legally forbidden to hide Jews. But it was legally permissible to kill them. What the law says must never be the basis of morality. And on top of that, the law is simply something that is determined as such. It can just be changed. In your words: we can easily define it as “not wrong.”