In Berlin, rent control isn't a fringe topic. Half of Berlin was formerly communist (the east) with the non-conformists being sent out to the sticks. And the other half has a higher proportion of (partly radical) leftists due to the federal draft not applying in Berlin (so young, mostly left-leaning, males moved to west Berlin to avoid serving in the military). So the general population in Berlin is rather more friendly to ideas such as communal property, rent control and generally sticking it to the evil capitalist man.