the return on capital (if any at all under mutualism)
Yeehaw! Thanks for proving my point that what you are advocating, even if it's not exactly identical to communism (as you seem to think), shares
exactly the same downfall.
The downfall of communism, and of socialism to a lesser degree (because socialism is just communism to a lesser degree) is that no one can profit. With pure communism, doctors and janitors get paid the same. Thus, there's negative profit in being a doctor compared to being a janitor - you put much more effort into it, and get absolutely nothing back in return.
If investors don't get a return on capital, as by your own admission would happen with your "mutualism", they simply won't invest. Why would I want to start of new business if I'll lose all the money I put into it if the business fails, yet won't see a dime in profit if the business suceeds?
where have I argued for collective ownership of anything?
There are individual rights and collective rights. This "individual rights in common" bullshit you won't shut up about is collective rights in sheep's clothing.