So to the knowledgeable, why should their credibility suffer?
Assume you are a guerrilla leader in some other country. Someone comes to you, claiming that they are supported by the Red Cross, and offering to take some annoying hostages off your hands.
Knowing what happened in Colombia, are you MORE or LESS likely to turn them over?
Suppose some fool has been going around loading vending machines with Coca-Colas that have projectile-strength laxative. The Coca Cola Company has nothing to do with this. But them you see a victim of this laxative Coke on TV.
Next time you are thirsty, are you gonna opt for a Coke? Or would you just have a Pepsi to be on the safe side?
Exactly.
It's not about the Red Cross not knowing: it's about the fact that they were used for deceptive purposes.