Except for political calls, I feel sorry for the telemarketer. They're in what's called a boiler room, lots of them, all making these calls trying to make a living.
So, much as I want to just hang up, instead I say "I'm sorry, I'm not interested, goodbye." and then I hang up.
Politicians exempted themselves from Do Not Call, so they're a different story.
When you order online that company now has the right to call you even though you have a DNC