They are so easy to root from cuttings I wouldn't bother with the seeds. You can do hardwood, softwood and root cuttings. But that's not what you asked! ;-)

I just hate to pull the seedlings and throw them away.

Nope, they do not grow true from seed. Seedling crape myrtles are usually a very poor substitution for vegetatively grown hybrid cultivars and you shouldn't feel bad about disposing of them.

However, I've had an exception or two crop up in my own yard that showed such promise from an early age that I kept them. There would be nothing deceptive about you potting the nicer of your seedlings up and labeling them as "White Crape Myrtle", selling them at the very low price one should expect for a seedling.

Thanks. I appreciate the info.