Moreover, if you do resist allowing people to take their own lives, when they are consenting intelligent adults, in obvious ongoing chronic distress, why do you think it is your right to do so?
For if you simply got out of the way, then all these people would be guilty of is offending you and possibly, your conception of a deity.
You do not have a right to not be offended, and certainly you do not have the right to prevent the offence of a deity.
Go on - prove your compassion isn't just words. Share in his life in a way that will make a difference, or leave this peaceful suffering man alone to make his own choices.
He's not asking you to kill him, he's just asking you to let him choose to die when and how he wants.
It's his life, not yours - and as he does not (and cannot) own your life, then stop trying to own his for your conscience or because of your own belief system.