If the conversation is about the original tweet, Islam is not a race to begin with.
No, it's a religion... but I suppose it could also more properly be called an ethnicity, as in "the fact or state of belonging to a social group that has a common national or cultural tradition."
As a point of comparison, perhaps you'll accept the differentiation between "Christianity" and "Christendom," as conveying the same basic idea.
The idea of assimilation -- or lack thereof -- has a lot less to do with the religion, than it has to do with changing the cultural traditions that have grown up around the religion.
If you look at the terrorists at work in Europe, they're the ones who have been "radicalized" by Imams whose main concern seems to be to fight back against the forces of assimilation. And they've sort of got a point. Let's face it: Western Culture is a lot more attractive (because it's better) to most people, than the sort of backwards fanaticism that characterizes the places ruled by radical Islam. After a generation or two of living within a vibrant and confident culture, one where Muslim women are treated as actual people, I think a lot of Muslims are far more Western than anything else.
Where that idea breaks down, is where immigrants' behavior is in conflict with basic cultural norms of the host country -- again, I'll point to how women are treated -- and the conflict is allowed to persist, rather than disallowed. But that's more a problem with the host culture.
