You mean from an animal welfare perspective? There’s a fairly compelling argument that using any animal products (at least ones that require killing the animal) contributes to reduced animal welfare. Yes, cow leather is basically a biproduct of the meat industry, but the leather market makes the meat industry more profitable.

>> but the leather market makes the meat industry more profitable.

you could also say it makes the meat cheaper.

Sure. Same thing

And large parts of the meat industry is a by-product of the dairy industry where I live.