So, the fact that something is popular does, in fact, make it normal. "Right" is a completely different discussion from popularity, that's correct.
Anyway, I generally agree we should minimize suffering as much as we can, but certain materials are irreplaceable for now. Leather has a combination of properties we haven't been able to match with plant or synthetic materials. There are fake leathers, yes, but they don't have the durability or flame resistance of real leather.
As for killing animals, I try to avoid it if it's not necessary, and try to do it as quickly as possible otherwise.