Meat is only ruined if the animal is stressed during slaughter.

Prior to that, for large animals like cows, only the last three months of feeding matters for the quality of the meat. Far less time for smaller animals.

Treating animals well has absolutely nothing to do with the quality of the meat, except in the few moments immediately before slaughter. We should treat animals well on a matter of principle, and that's basically the only argument there is to it.

To be clear, I agree with that principle.