Ah the robo call....
Gotta hate it but the only ones I get here in MN are from organizations I've willingly joined.
Now door knockers, that's another story. I used to do that job for four years running different canvassess on different issues and elections. Interesting work, gives you an interesting insight into your town and the people that live in it. Also, I have tough skin from getting yelled at so often. Anyways, if I don't have the time and I don't agree with them I'll just be polite, offer them some water or a bathroom and ask them to leave. But if I got some time to kill and I don't agree with them it can be fun to mess with them and play devils advocate. I get a kick out of it, I learn something new from the way they think and it keeps them from getting to more doors that night. So, if I have the time it's win win!