... I find berlin the most liberal place in the world and feel 100 percent safe here. All central districts are quite heterogenous. Berlin is a city OF foreigners. You hear more english, spanish, italian, french - and of course turkish - than German in some areas. Berlin is also full of jews... Many comments seem to be fueled by old prejudices.
And of course there are less black people in Berlin than in Paris because Germany did have so many colonies in africa like france... this has nothting to do with racism - on the contrary. my parisian friends who live in berlin always are amazed how safe berlin is. in paris you can be attacked in a bus easily - no matter if you are black or white - while this never will happen in berlin.
belrin is famous and proud for its diversity. that is why people move here and love it.
marzahn is not really liberal. it is an ugly neighborhood with germans and many russians - many of them unemployed and without higher education. but there is no need to go there, there is nothing to see and it is far far far far remote at the far end of east berlin.
the mayor of berlin is openly gay (since 2001 in office), there are some turks in hight political functions... berlin is very left wing and you can run naked on the streets and people would find it ok.
so no worries, you will feel free in berlin and for sure, you will love it like anyone else who moved here. (only if you are conservative or right-wing, then you might not like it).