I'm annoyed, but they're just trying to earn a paycheck. I immediately say no thank you, but not rudely, and close the door. Why waste your or their time? The less time they spend talking to someone definitely not interested, the more time they have to find someone who is. So it's not rude to be direct.

If they're religious or not my political persuasion, and I'm not busy, I engage them. They'll never convince me. I'm not going to debate them, no point. But the more time they waste on my doorstep, the fewer people they'll bother.