I don't want capitalism even if it works
for the same reason I don't want to live in an authoritarian state, even if my quality of life is good.
I believe in the right to self determination. For myself. For other individuals. For our communities. And for our society at large.
Large-scale capitalist firms, run by small boards of elites, owned by shareholders, do not provide self determination. These are top-down control structures.
We have some ability to influence the decisions these companies/elites make by "voting" with our wallets, by submitting feedback to customer service, and by lobbying legislators where regulation is important. These things matter and should be done. They can help improve what we have.
But these tactics, under a capitalist power structure, still put the power in the hands of the few, in the hands of the people at the top. I want to take away their power and democratize it, spread it to the people.
In some cases, this would be in the form of worker-ownership or community ownership of factories. It would involve less vertical integration. It would involve, even, small capitalist firms like local restaurants or repair shops. It would still involve markets. It would also involve some central planning, at least with certain industries like health care. It could come in other forms - I'm not really that stingy about the exact implementation, as long as its democratic.