Would this be morally wrong? I really am at my wits end with this.?

How about you just put up a sign that says no religious solicitation ? And put it right on the door so they don't try and use the excuse that they didn't see it. That way they don't think you're singling them out. Me personally, even though I am a born again Christian I would just be very stern with them and tell them to please not knock on your door, but say it in a very serious stern voice, and if it happens again I would start being rude and threaten legal action. God bless.