Because if you believe in "Satan", you also believe in God, and they would more than likely use that against you, given a "Satanist" isn't aware of his own beliefs, as contradictory as they are subject to being.
I have no respect for a religion that advertises their beliefs like some stupid telemarketer or magazine salesman. They're annoying and it's tactless to go around advertising your religion to other people.
The fact that it's part of their service is irrelevent to the fact that it's ****ing stupid.
I'd also like to add :
C) Tell them to stop coming to your house (I'm sure they'll respect that and listen)
noone from jehovas witness knocks on my door anyway, so I cant share in your despair.. I believe its not just jehovas witness doing the door to door nonsense.. mormans and other christian groups do it as well.
I know there are hard headed religious zealots in the world, but they all have to listen if you tell them you do not want to hear it. I believe in the bible it mentions jesus saying something to the effect of "Let them come"... bangin someones door down isnt lettin them come..
JW's deal mainly with the book of revelations and consider jesus to be a seperate entity from god [ just as you are considered a seperate entity from your father/mother ]