"If you think capitalism is the cause of so many deaths in the world, what are you doing here in Steem when you could do the same for free in other platforms?"
I see a few main points here. Commodification, and a complete non-understanding of socio-economic systems.
Capitalism must turn everything into a commodity to be sold, capitalism cannot exist without continuing to create new markets that can be exploited. LGBT pride has been consumed by this, with all these neo-liberal corporations putting pride colors up and being praised for it, even though they didn't actually do anything. Commodification does not only make everything fake, it also lowers its social value, because it must be turned into a form that is exploitable.
Capital gains are not the only reason people do things. People create art because they like art, people become doctors because they like helping people. I am on steem because I have a chance to use capital to grow power and spread knowledge faster than other social media. If I found another that was better, but had no profit, I would jump ship in a heartbeat.
People need money to survive under capitalism. You can't just "do stuff for free", thats not how it works. To quote the million ancaps on this platform "learn economics". (A joke.) Communism isn't doing everything for free, communism is planning how to most effectively distribute resources between workers. The most common form of this is simply being able to take what you need and giving what you can, which is much different from working "for free" under this economic system.
I cannot just wish capitalism away, working towards it through my own labor in small ways (like writing for free) is not realistic. I think this video below sums it up nicely