I have a real problem with the whole "If they run into a male in the wild" argument. What if I asked "Is it ok for me to feed a mouse my neighbor caught in a mouse trap to my snake?" The same argument could be used to justify saying "yeah sure, feed the mouse to your snake, after all, in the wild your snake would eat any mouse it found, not just the parasite free ones."

At the end of the day you have to make the call to breed or not to breed. I think weight is important but like Freakie_frog says, health, fat reserves, age are all important too. Relying on what would happen in nature is not always best. Nature can be a cruel, unforgiving witch.