That's not dumb, it's a valid position and one I shared for many years, especially in regards to rabbits. Some reasons for crossbreeding include "hybrid vigor" where the Cornish Rock chick grows faster than its Cornish or Plymouth Rock parents, and the opportunity to make a custom flock with the attributes one values. So, in my case, I'm (hopefully) not making "mutts" as much as tweaking the flock a little. In a few years, I hope to have a robust flock of slightly-larger-than-SOP Black Australorps. I don't show chickens and my stock was hatchery quality to start with, so adding superior quality BAs would be an unnecessary expense..... in my case.