While that inb4 is wrong, it's not even racist, that's not the point to attack.
Stop using always the "easy" way out in discussions, go for the core of where exactly your opponent makes his mistake.>Great, the naysayer is a racist, I'll point that out, and completely disregard all the points he tries to make in his argumentation.
That behavior is really a disease that exists all over the world these days, and ultimately gives more power to "extremists", that won't socially kill people over minor slips like that. (Who exactly is even the extremist there?)
You make yourself look like an ideological brainfart to other people, while you yourself are convinced that's the person on the other side.
The way to argue against that inb4 is that Europe is anything but "socially homogeneous". They had a large immigration wave in the 50s and 60s from, for example, the Middle East. And even the people that "always" have been there are not equals. Differences in income have exploded since after WWII (due to US American influence).
Yes, European countries are smaller than the US (as a whole), but there always have been long-running trains. Currently the EuroNight Moscow - Warsaw - Berlin - Paris sticks out.
And if you extend your view beyond Europe, then there is the fucking Transsib. Anyone calling that "small" has no idea what he is talking about.