I see nothing wrong with ignoring a call from a deliberately blocked number, unless I'm expecting a call from someone who has warned me their number is blocked. I wouldn't answer the door for a person with something covering their face. I wouldn't say anything that could be held against me to a person who won't give me their full real name. This situation is no different. If you expect me to engage you in any way, it's only fair that I know exactly who I'm dealing with and can form some preliminary notion of why you want to talk to me. Otherwise all the cards are in your hand, and I can be forgiven for assuming I'm being taken for a mark.
Because sure enough, many calls from 'unknown' or 'private number' that I've answered, have indeed been people trying to pry money from my hands.
If it's someone I know, they can leave me a message. If they get annoyed I don't answer, all I need to say is, 'How was I supposed to know it was you?'