You could breed them, but I doubt you'd be able to find enough people to sell them to. That's why you can find them so cheap at places like flea markets, sitting in a pale of dirty water or in overcrowded conditions. And more likely than not, since they are so cheap, the people who buy them will put them in one of those tiny cheap plastic critter carriers and eventually lose interest in them. Or they will wonder a week later why their little precious has stopped eating and moving (answer: no heat, no UV light, no filtration, improper feeding, not enough space, not enough water...). Not trying to be harsh, but the reality is, it's probably more humane not to allow any eggs to incubate at all. The section on reproduction on this website says it all, really.
http://redearslider.com/reproduction.html