Huskerlife, you do make a fair point. It's entirely possible that he would do the same thing as his brothers given the opportunity.
An argument can also be made, however, that if he were offered he would not want to be lumped in with his flaky brothers and be solid in his commitment. I guess there is some middle ground to be found here. Just as you rightly claim blind optimism is foolish, I think it's equally foolish to say he will screw us over, guaranteed, if given the chance, which seems to be what you are suggesting.
I have no trouble not offering him a scholarship (and it sounds like we already have our eyes on bigger fish, so it may be a moot point) but if the coaches do offer him, I still say it won't be a fireable offense.
I'm the youngest of four in my family. All three of my older siblings flunked out of college. Should I not have been given the chance to go to college? Fortunately, my parents didn't follow your logic here and they sent me to college. I graduated in four years, then went to graduate school for another four, graduating from there as well.
This is the point I and others are making... You can't automatically assume that baby brother Gabbert will do us like his older brothers.