Vegitarians/Vegans with carnivore pets.

I used to know a girl who's family were strict vegitarians, they had 2 or 3 cats and because they didn't eat meat they wouldn't let the cats eat it. They fed them on bulger wheat (unsure if that's spelt right). Apparently when the cats got older they would try eat meat but would be extremely ill if they ate any. I always thought it was really cruel to go against an animals natural diet and instincts but they seemed to think it was perfectly justified. In my eyes if you don't wanna go near meat you don't buy an animal that's diet has meat in. What does everyone else think?