They're paying customers, seems like they have as much a right to sit down as anyone else. For that matter, they occupy that seat for a shorter period of time

They're paying customers, seems like they have as much a right to sit down as anyone else. For that matter, they occupy that seat for a shorter period of time than someone eating would, too. Most of the 'full' places in America, especially more casual places where there isn't waitstaff that reconfigures seating for every party seems to have a lot of underutilized tables. One person sitting at a table for four is common, and sitting next to that person is seen as awkward. That table is "Taken" - and in a lot of ways, I understand; I'm an introvert, too... and sometimes I'm not really up for conversation with my lunch. But, I find that reading the internet on your phone (and by extension, using an e-reader) are a lot more acceptable than those sorts of things used to be. With those affordances, I think it's easier than it used to be to politely say "I'm not really up for conversation today"