Because the entire tipping culture is based upon shame if a non-insignificant amount of people feel that they are expected to tip whenever asked for a tip, it ends up being the the same as if there was an actual social obligation to tip. Then there can become one.
*There actually is a social obligation to tip counter staff - only if you're ordering an alcoholic drink though.
You're right about bartenders being the exception. That I tend to view more as a outright bribe for better drinks and faster service which is honestly not ideal either.
I do think businesses are taking advantage of our guilt and conditioning to try to normalize tips where they never existed before. Hopefully your friend can be brought around to see that. The fewer people who accept it, the slower it will spread. I really hope "tip creep" pisses people off enough that we start to question the entire culture of tipping.
False! In my locale waitstaff make the same (high) minimum wage as everyone else.
They want to push the perception that society thinks you should tip for counter service, but it's not real (at least not yet). I don't tip for carry out or for retail transactions. Tips are reserved for people who perform a service (waiting on my table, cutting my hair, etc) and not for every employee I interact with who handles food.
There was an exception made at the height of the pandemic for restaurants that had few if any indoor diners. We tipped them for carry out because it's money they would have been getting if it were safe to eat inside like we wanted to. Now that most people are back to their old habits (safe or not) I think it's fine to stop tipping for carry out orders.