The problem is the whole rego thing is an excuse for a behaviour, not a reason.
If you wanted to get into "rights" to be on the road, the correct place to look is the road rules, where it states, unambiguously that a bicycle is a vehicle permitted on the road. End of the "deserve..." "rights..." "should.." arguments.
The whole acting like a prick to bike riders because they didn't pay a registration that doesn't even exist (hence even if the cyclist wanted to pay rego and wear a numberplate, they can't) is simply an excuse to act like a prick.
Arguing the point with them isn't going to work.