Because people believing in great replacement theory take existing issues (falling birth rates due to worker hours/absence of socialized childcare, immigration workers hiring to dodge worker rights) and arrive at weird conclusions. Propagandists are obviously unreachable as they are paid to lower wages of immigrants, but people who believe in that stuff? they see issues, they can be reached. this is all of course in personal conversations, without peer pressures, and not a duty of marginalised comrades.

Re: larger points there are two sets (well lots more than two, but two groups) of heuristics of looking at the world: the elite one and the marginal one. The elite one is squabbling about who should be in the elites and the marginal is elites shouldn't exist (communism/anarchism).

The elite one is acceptable to the masses of workers as long as they deliver on something of livable standard (like why communists collapsed in usa after ww2), and following squabbling of slowly removing barriers on entry to elites to woman/blacks/lgbtq.

But fundamentally that system of deliviring living standards is unstable due to larger arch of history of capitalists profit drive, and we now entering the zone where they have consistently not delivering for larger and larger slices of population who start asking questions. Those questions lead them to all sorts of answers , some think its cause christianity, some cause one of the groups entered the elites, some cause outsourcing to china; some think cause thats what the capitalist system does