Is it right for credit card companies to ask for your social security number so that you can opt out of receiving credit offers?

I receive way too many credit offers. I usually just tear them up and throw them away. But it’s such a waste of paper and it really annoys me. I looked at one American Express one and at the bottom it says…“You can choose to stop receiving “prescreened” offers of credit by calling toll free 1–888-567–8688. So I called the number and it was an automated system. It said that by answering a few questions I could opt out of receiving any type of credit offer based on my credit report. I answered the questions regarding my name, address and phone number, but then it asked for my SS# and I hung up. Why would they need that kind of information?? That does not seem right or safe. I do not see any logical reason for that…..