Indeed, and I am sure we all do that.
Evidence suggests that not everybody does though - just have a look through Preloved etc and see some of the tups being sold for breeding that really should have been burgers. We certainly fell into that trap with poultry early on, and bred some real crap because we got carried away by how cute the chicks were!
It's oh so difficult to buy well until you know what you're looking for though, especially with older animals. We sold a few older ewes last year who would have made a cracking starter flock, but they were all ewes who we'd have gladly kept if only we had the space. This year we'll be getting rid of two ewes, but they'll be going for mutton, since I refuse to pass on known problems to somebody else.