Um, how are they not supporting the 2nd Amendment or even attacking it for that matter? They're not saying NRA members or even gun owners in general can't fly on Delta planes anymore.
It's a private company, it they want to give discounts to certain other organizations, they can. What they can't do is go "AAA members can fly, but AARP members can't"; that hasn't happened though. NRA members can still fly on their planes.
Interesting enough, the mayors of Virginia, New York and Alabama have welcomed Delta to move to their state. Hopefully this happens. Other states are likely to extend the welcome as well.