Racism does exist in the respective countries of those three cities but probably not directly in those cities, although in Barcelona there is a growing hostility to tourists; the anti-immigrant/xenophobia sentiment is more prevalent in Eastern European countries I would say, ironic as huge swathes of those populations have emigrated to Western Europe and in turn face anti-immigrant attitudes.
In Barcelona a must is the Thermas sauna which is full of rentboys.
I would echo that a visit to Laboratory in Berlin is a must if you are looking for debauchery, I thought I had seen it all until I paid a visit to that place!
As an aside if you are looking for something a bit different and a respite from debauchery in Berlin and you are there on the last Saturday of a month,I can recommend the following club night that is full of Turkish & Middle Eastern guys:
https://awesomeberlin.net/party/gay/gayhane/kreuzberg