From a ACM perspective - It's a lesson that was learned in Vietnam, that apparently might have to be learned again. The F-4 originally didn't have a gun because now that they had the new fangled missles, they were good. What about when you're inside the min range of your missiles? What about when you've shot your wad WRT missiles and have plenty of go juice? You disengage and run for the hills?
Disengage and run for the hills... yes. We're not in the age of Phantoms shooting AIM-9Bs... Do you honestly think ANYONE would want to take on any sort of an air to air fight w/ an opponent who would more than likely have an AA-11/Equivalent missile? Bluster aside, I'd turn tail and bug out. And that's assuming you would get into a position where you'd be able to launch all missiles w/o burning up all your gas.
Yeah, you may get closer to AAA - but that's why we get paid the big bucks. RCS is worthless if you can't do your job, which is support the guys on the ground.
Having a gun is vital in my mind. I think it is a significant loss of effectiveness. But I'm just a dumb helo company grade.
If your aircraft loses that RCS, how does that affect it's ability to preform it's mission in the future? Maybe your gun pass will cost that airframe it's ability to do another mission down the road, more vital.
Again, I'm not an anti-gun kind of guy; I argue solely for the sake of being devil's advocate.