Question

Why did Karl Marx condemn capitalists

Answer 1

Karl Marx believed that capitalism would eventually stagnate due to contradictions and will eventually lead to socialist policies. He also thought that the only way capitalism could be overcome was via revolution. (As Marx thought everything else should be settled by)

Answer 2

He believed that the better way for a community to live is for them to all share their wealth such that you didn't buy or sell things.  Capitalism is nearly the exact opposite of that where you work for money and buy stuff with that money, no communal ownership