I have to agree with everyone else. I don't know if anyone else has had this experience, but I've volunteered in shelters before. The majority of dogs are pure bred dogs- mostly labs, to be honest.
It is so heart breaking- you can just look at the dogs and know they're wondering where their familes are, and why they're alone...They have no idea that they're going to die alone.
To think about it, ALL of those dogs were wanted at some time by some person- maybe they were the cutest puppy at the time.
The sheer volume of pets that spend their last hours in a kill shelter are astounding.
Now, bearing that in mind, unless you have a darn good reason to be breeding- such as you know your dogs are the top of the game, then there's no way you should be doing it.
And, the ONLY way you know your dogs are the best is if you COMPARE THEM TO OTHER DOGS- the whole purpose of a dog show is to test breedworthiness.
This is just my opinion, and I know its a strong one. There are other reasons not to breed, like expensive it is (when done right) and the risk of putting your bitch in jeapordy.
When/If my pup is ever bred, I will not put her life on the line unless she proves to be an excellent example of her breed. Otherwise, she will be spayed, which is also fine with me. She's a great dog (I am a biased mom).