I think so. Nobody who doesn't believe in it should be forced to participate, but if somebody wants to die then let them. If they dont want to suffer anymore then why should we stop them.
If you were a soldier at war and your friend got hit and is bleeding to death with no medic in sight, and he asks you to kill him, what would you do? I probably would end it if he wants me to. If there's absolutely no way of saving him and he chooses it rationally then than soldier scenario is pretty much the same as the incurable disease one. But somehow the soldier scenario tends to be more acceptable because of the urgency of the setting but the moral choice is essentially the same.
If you know you're going to die then why not face it and at least choose the day you die and how.