A barber/hairdresser will get paid minimum-wage over here in Germany. From friends who worked in this profession I know that they make even less at the end of the day, roughly 5€ per hour. Only because you get paid market-rate doesn't mean you can make a living.
Whenever I ask myself if I would be happy to receive a tip being in the same situation I tip: restaurant, package delivery...everywhere.
Nothing specific to the US.
I'm from Belgium, so we do not have a tipping culture either, and in many cases it is not that needed, but always welcome (restaurants). I live in a university city, so many of the waiters are students and as having been a student in a similar position, I know that they do not tend to have money to waste so the tips are a nice extra.
In general I am happy that we do not have a strong culture around it like in the US, because then you'd have to find out how much to tip etc, which would probably be uncomfortable for me.