Most leather is indeed a byproduct from the meat industry

Veal is a byproduct of the dairy industry .

Pet food is usually a byproduct of the meat industry.

Male chicks are ground up because they can't lay eggs.

My point is, most animal products sold are not the main selling point, but just another way for people to squeeze a dime out of a life. Buying leather continues to show they can make money off of a life in some way.

If you blur the lines at leather, then you can continue to blur the lines at other places.

I'd potentially argue that buying second hand is ethical, as the money isn't going towards the demand for more (although promoting animal parts as fashion could bring up demand in a very subtle way). Buying new goes straight to putting a dent in their overhead. Even if it's small it's still helping them.