I have both Florida blues and red sided...(amongst others!) I asked out of interest a while ago the same question, and basically, if you breed them, firstly they are not as likely to produce offspring being different sub species, and then secondly, if you are lucky and get young, you are likely to get some not so bright babies that you end up being stuck with cos no one wants a mongrel!!

the 'purist' argument as mentioned is basically if you do sell the offspring...what do you sell them as? and who stops the new owners from breeding from it and selling as pure breeds etc....(hence the purist thing...they want pure breeds!)

anyway hope that helps...