[somenameforme]

But it's not really "Germany" calling the AfD fascist, in fact ever more Germans are voting for them. Rather the people who don't like them are calling them fascist. You're effectively describing an effect of extreme polarization, where 'the other side' is demonized in ways with, at best, tenuous connections to reality.

I think your post hits on the primary cause of polarization: incompatible ideologies. One group in [some country] want ever more immigrants, regardless of the cost or quality. The other side wants to limit immigration to skilled and educated migrants who are expected to learn the local language and integrate into society. These two sides' views are different enough that it's pretty tough to get a meet in the middle, and the issue is relatively urgent, so you get polarization.

Of course this leads to nasty online conversations where you might have one group talking about the crime rates of new migrants, while the other side calls them racist or fascists for doing such. And I would agree that this probably contributes to polarization, but it's also an effect of an already existing polarization, rather than anything even close to a core cause. Europe's had no difficulty polarizing plenty throughout history, long before the internet. It's just for the past ~80 years we've all been living in a little bubble of relative peace, tranquility, and growth. And I think that bubble has popped.