While we would never condone the wearing of fur, we happily wear black leather most of the time.
The reason we are anti-fur is the usual - we don't like to see these creatures killed so their coats can be worn. A great anti-fur campaign had some tart wearing a mink stole, the caption reading "one fur coat, two spoilt bitches". Which about says it all.
As for leather, the cows are bred and killed for their meat. The leather is a by-product. So making clothes and furntiture from it is just using what would other wise be wasted, so it's practical.
Veggies of course argue that we shouldn't kill the cows for food. However, all those herds are bred for food, they are not caught wild. If we didn't eat meat, the cows would never be bred, so would never exist in the first place.