If you don’t own something that earns income without you needing to work for it, then you’re not a capitalist.
The majority of people, even those living in the most capitalistic countries are not themselves capitalists.
Earning income from the things one creates or acquires using the existing currency is not unreasonable or unfair though. Income from assets and capital gains from growing popularity or a naturally forming scarcity are not significantly problematic either.
It’s fractional reserve banking that unfairly gives a privileged few control of new currency creation… and the privately owned central banking systems which issue credit backed by nothing — those are the real problems.
Banking related capital gains result from the deliberate devaluation of the existing currency by increasing the supply. New currency creation and its distribution benefit the ones who get it first and it harms the rest.
There is a top-down system design advantage that benefits the bankers, the ruling class, and others who abuse the effects of new currency creation. They are increasing their share of wealth by stealing the value of the already existing currency that is held and earned by everyone else.
The institutionalization of banking systems that are designed to cheat and steal isn’t any “ism” it’s just plain old theft.
You don’t need to be a socialist to be against a rigged banking system, and to be clear — socialism has its dark side too.