The other issue with this is that sometimes people don’t tip servers because they liked the service / want to support underpaid staff / etc. People will tip in

The other issue with this is that sometimes people don’t tip servers because they liked the service / want to support underpaid staff / etc. People will tip in these situations because they want to be perceived by others as good tippers. This is why those flip screens broadcast your tipping decisions to the entire line behind you and everyone you’re with—capitalizing on peer pressure. I’m sure that if there was a separate tipping voting booth where nobody could know your tipping decision, tip income would crater.