Absolutely this. Our conditioned phone etiquette is abused by these sorts of people. Once I've determined that you don't offer any value to me and aren't going to offer any value to me, I will say "I'm not interested, goodbye", and hang up. You don't feel any obligation to read the entirety of a spam email before deleting it, do you?

This might make me rude, but it sure makes dealing with cold-calling spammers a lot less irritating and time-consuming.

I always like the simple "Thanks, but no thanks" followed by immediately hanging up.

This is apparently a good idea, but it justifies the recruiter's methods: if they can rely you hanging up quicker than the extra time they would spend on proper research.