I don't do them, or teach them, either. I don't deal with lenders in any way, shape or form. You have to close, or double-close, when flipping REO's. If your buyer flakes out, you're left holding the bag. You leave the lender hanging, and they won't deal with you anymore.
But, with that being said, there are a bunch of people out there making a lot of money in this field. Similarly, you wouldn't catch me dead try to short sale a property. But, people are out there making good money doing this, also. It's just about preference.