So that they can make arguments like yours when called out over it, and deny that they are being racist pieces of garbage engaging in propaganda techniques
They are hampering their own message because they don't want to be called out for holding that position?
No, because they want to have an excuse to point to when they inevitably are called out.
It's not dissimilar from "I've heard some people say..." as a caveat to a statement. In
that dishonest shielding statement, the idea is that someone posts their view (or a straw man view) as if it was not their own (or as if it was someone specifically) and then when the other person says "that's racist!" (Or "that's not what I said") the interlocutor can then say "I never said that was what I believed" (or I never said that's what you believed"), and dance away from the accusation of being a racist (or straw-manning).
Similarly, "extremist muslims" is a way of painting muslims as extremist in a way that will impact minds to think muslims are extremists, while at the same time having a position they can dance back to when people point out "not all muslims".
They then emerge from the exchange having made the equivalency without having to explain that they are drawing equivalancies.
Isn't rhetoric !!FUN!!?