I'm on the Do Not Call Registry, so... anyone who's calling me, that I don't have a pre-existing relationship with, is breaking the law.
I will be polite, with those who remain who do, up to a point. It's mostly charities, often good charities, and as some have said, they're just trying to do their job. I don't give anyone money over the phone, because it's not behavior I want to encourage, but I get it.
As for the people who call us about twice a month with the "...this is your credit card company..." robocalls, though...
No, you're f@$%ing not. If you were, you would know who my credit card company was. You are a willing accomplice to fraud, and no amount of "just doing your job" justifies that. Occasionally, I go through to a person just to talk to them about the federal penalties they can expect as an accomplice to fraud.
If those people go home and have nightmares, well, good.
But just speaking in general: when you call someone on the phone, you have a captive audience who really can't do anything else while they're talking to you. You don't know what you're interrupting. If you don't respect that, you're either abusing someone who was actually raised to be polite, re-enforcing behavior that causes people to be less courteous to strangers, or both. I know telemarketers are trained in all sorts of rotten behavior, from that false "How are you doing this morning/evening/afternoon" to refusing to give up before receiving a certain number of "no"s, but that doesn't change the fact that following that training is actively making the world a less courteous and more insincere place.