I think the notion that 'capitalists are evil exploiters' comes from the fact that it's very visible for the public that the workers are working their asses off, while the capitalist 'is doing nothing' and get even more money.
I think they don't realise that the capitalist isn't making the worker 20 or 30% more productive, but 10 or 100 times. The capital provider (capitalist) actually caused 90 to 99% of the productivity, that's why the market rewards him more.
Think about a taxi driver without a car, a magazine worker without a fork truck, a fishingman without a boat or even an accountant without a calculator. Because people don't realise this, it's mostly invisible for the public.
So people see the worker work hard, while the not working capitalist gets more money. A perfect issue for politicians to gaslight people that the capitalist is evil and tax the hell out of him, and socialism is born.
P.S. this all is about a free market, once the capitalist start to lobby and use the state to get unfair advantages, he's indeed evil. But this isn't capitalism, it's statism / fascism.