"In Germany, the population is more concerned about privacy. Despite being targeted by a string of communist terrorist attacks in the 1970s and 80s, it maintained an open system, without any faregates at any train station (including subways); fare enforcement in German cities relies on proof of payment with roving inspectors. "

A lot of systems have faregates that work also using anonymous tickets or fare cards.

But kudos to Germany for using such a system, I cannot imagine it working without massive fare evasion in many other countries.