Yes, it must be one of the foreigners, because all Poles speak perfect Polish
No, not all Poles speak perfect Polish, but when they are semi-literate or stupid, they make mistakes typical for native speakers, they might spell "dżewo" instead of "drzewo" for example, but not mistake a "na + noun" structure with a "do + noun" structure.
Poles could possibly ever be racist enough daub any racist graffiti anywhere anyway.
I never said that. They do that, a lot, e.g. "Żydzi do gazu", "Biała siła", why not? I just haven't seen that much graffiti employing the word "Murzyn" as it's not generally perceived as pejorative, esp. not in the less educated circles of society. I asked for pictures of graffiti and got one, plus info about "Murzyny do drewa" which is definitely not a native Polish effort.
I have never said anywhere that Polish people are never racist. I have, on the other hand, claimed that the word "Murzyn" is not racist. Of course, with time and patience, the "progressive" element of Polish society will force us to accept that it is now officially racist, and make us replace it with some monstrosity such as "czarnoskóry" ("Blackskin") which, when we compare it with "Redskin" which has been banned as racist, does not sound all that great either, does it?