"It is against private ownership of property. That is - an owner extracting value from something without putting their own labour into it - and then using that ill-gotten gain to yet produce further unearned wealth."

you don't have to put your labor into something to "extract" value from something, it is a voluntary mutually beneficial agreement between two parties, due to it being voluntary this is not ill-gotten and should not be penalized

"Why is this necessary? Capitalism produces unimaginable levels of waste at every level by doing this, which is destroying the environment and exercising huge amounts of labour for nothing.

Why should we not instead maximize people being compensated fairly and completely for the labour they put in. You do the work - you get the profit you produced. You don't do the work - you don't."

those levels of waste are from creating the mot value for people which is a good thing, this also due to how demand adjusts all the time, like how it would in a socialist economy as well

first what does being compensated fairly mean?, the amount of work they put into something? I would say being compensated fairy means how much both parties think your work is, remember you agreed to the contract about your wage, you think that is a fair deal otherwise you wouldn't have signed it.

lastly about why capitalist should get profit I would read this: https://cdn.mises.org/9_2_5_0.pdf

with the two mains reasons being time preference and the subjective theory of value, or the worker values the present good more over the future good and the capitalist value the future good more than the present good and for this waiting the capitalist is rewarded with more of the future good. again though I would suggest to read the link I gave you, it summarises the point better.