I don't know if I agree with you on this. It is because the Red Cross is an impartial organization that makes them who they are. They're willing to help anyone, anywhere and they truly are humanitarian. I know that the Taliban doesn't fight this war the same way that we do, and I find their tactics appalling as much as you do. That doesn't make them any less human.
The Red Cross has a long history of working in and with the countries we are at war with. During the second World War, the Red Cross was allowed access to allied prisoners of war, as well as access to the American's EPWs. It's a give and take situation, and it doesn't always look good, but that's how they have to operate in order to maintain their impartiality. They are also mentioned in the Geneva Conventions, though not all countries abide by these accords.
I suppose I see their working with the enemy as a sign that I might have a chance at getting a message out if I'm ever captured. I know it's a very dim hope, but at least the Red Cross is doing their part to ensure channels are open.