“That’s a fair point. Let me put it this way, as you did in the last sentence - you and I are not going to know the symptoms of someone we are in close proximity unless they are actively coughing or sneezing. They could have a fever and we would not know that, or if they have been coughing /sneezing previously and are not while we are around them.”
Let me put it this way. Unless I shake hands with them, and if I do then do not wash my hands, and unless I share any body fluids with them, or other not not safe things, I am not going to get infected merely breathing the same space they occupy.
Your hands, protecting them and not touching other surfaces with bare hands, is far more important than any mask you think will protect you from just breathing the same air as an infected person.
One of the doctors in China, who had not been to Wuhan, caught it from a doctor who HAD been to Wuhan (this was back in January, btw), merely by sitting at the same table as him at a conference.
Nice try, though.