Many, many, MANY reasons to not breed your dog. I've had VETS tell me I should breed Gryffon because he has such a good temperament, but I will not: I've been involved in GSDs and training for many years now, but I don't feel I know beans about responsible breeding.
And a mixed breed? My previous dogs where mixes from the shelter. They were wonderful dogs, and I still miss them deeply. I couldn't believe that people would give away, give up, dump such wonderful dogs, but it happens all the time. Your family and friends can find that perfect companion in the shelter, that is a win-win situation.
The trainer with whom I started with lost a favorite bitch during a whelp - he hasn't bred a litter since.
I remember one particular member on the board who posted proud pictures of his puppy, saying that when she was old enough, he was going to breed her. People tried to gently dissuade him of course, and must have been hurt by the lack of support, he didn't post again until about a year later, in the "In Loving Memory" section - his dog died trying to give birth.
It can happen.