It's almost flipped how the US and Europe have dealt with threats. The US has a long history of organized hate groups having the run of things. I don't Europe has experienced anything like the KKK for as long. However Europe is not far removed from fascist and authoritarian regimes. So things are more fresh in the minds of citizens and they are more likely to fight them. However when attacked through another method it subverts that and allows tacit approval from the public while their neighborhoods are transformed for the worse.
It is true, we have vigilante groups going around sometimes acting violent against people they think are immigrants, it is a real problem. It isn't all across Europe, and it isn't super common, but it happens, and that's enough.
I think the difference is in who is coordinating these efforts, because none of those vigilante groups are the country's own border patrol doing that in "official business" capacity, they're small groups of individuals usually associated with some far-right political groups, rather than tax funded government groups.
If the latter were to happen, you can be pretty sure people wouldn't put up with it, because most of us realize what's coming after that, because we were all forced to study history growing up.
> So things are more fresh in the minds of citizens and they are more likely to fight them
Yeah, this seems to be a big factor, most of us here (Europe) still have parents (and grand-parents) who remember and witnessed a lot of awful shit, and growing up would immediately reprimand you if you just pretended to like that, or carry thoughts in those veins.