When I answered, nobody replied.

I have entered many numbers in my address book, even spammers, so I have a record of the number.
Personally, if I don't recognize the #/caller, i don't pick up but, it would be great to have a button that just blocks all robocalls regardless of source. I get the "free speech" rights of "legitimate" callers argument but, free speech starts with the right to not listen. In my home, on my phone, my right to not listen trumps any others "right" to assault me against my will.