Please explain to me why capitalism is a good idea?

Ive looked at some of the previous posts on capitalism and the discussion about it on this sub strikes me as "suspect and confusing".

In the previous posts I've seen on here the first response to this question is usually a point about theres not a clear understanding of what is meant when the word capitalism is mentioned so to define my specific understanding:

"Capitalism is a system where private individuals own and have control over the means of production and extract profit from it."

Now what this boils down to in my head and sounds completely incoherent to me is that essentially:

"You pay wealthy people to do nothing but own capital and extract money by virtue of said ownership and sometimes they with no qualifications get to abuse that power"

I own stock of companies. As far as I can tell I'm a parasite. They pay me dividends, the money I spent on the stock went to the previous holder not to that companies R&D department.

Can someone give me the actual data and arguement as to why giving me passive income while I thoughtlessly bed rot off the backs of other people is good for the economy?