> As stated, it would justify "pay what you feel like" for every other good, to some extent.
That's true, except in the United States, in the case of delivery people and servers there is an extremely robust societal norm to tip. Such a norm doesn't exist for most other transactions.
That's a completely different argument from the one you gave before, and it's a justification for "why to tip, given the system exists", rather than "why this is a good system", which was my original question.
Your question was "What difference would it make if done as a regular delivery fee rather than [a tip]?", which was precisely the question I tried to answer. That is, you can't aggregate a block of voluntary exchanges and average the price.
The question was, why would a system tipping be better than a system of flat, honest fees for delivery. It does not address that to say, within this system, you should do this.
You were giving justifications at a system level, which why I said it would imply that other systems should shift to "pay what you feel like", irrespective of which ones currently use it.
And it's not an exchange, if one side has nothing to withhold, but a gift.
That's true, except in the United States, in the case of delivery people and servers there is an extremely robust societal norm to tip. Such a norm doesn't exist for most other transactions.