Here's an attempt to steelman just one of the things you bring up: the great replacement theory.
The United States, like many developed nations, is experiencing a fertility crisis: it doesn't produce enough families and resulting children to sustain it's current population.
The US could take steps to address the underlying problems that result in declining fertility for it's current population, but it's unlikely to do so for several reasons that all boil down to political realities where the people that are most incentivized to vote (retired people who earn social security) would probably bear the brunt of the (significant) costs of such solutions. See the idea of "concentrated benefits, diffuse costs".
So instead the US uses immigration to fill the gap left by declining fertility rates (an option not equally available to all developed countries), resulting in young US citizens continuing to struggle to form families, and producing a fraying of the social fabric that such an inability to form families is likely to have on a society.
So you can see why some people would be duped into such a conspiracy theory, which purports to explain what people are seeing with their very eyes.
The United States, like many developed nations, is experiencing a fertility crisis: it doesn't produce enough families and resulting children to sustain it's current population.
The US could take steps to address the underlying problems that result in declining fertility for it's current population, but it's unlikely to do so for several reasons that all boil down to political realities where the people that are most incentivized to vote (retired people who earn social security) would probably bear the brunt of the (significant) costs of such solutions. See the idea of "concentrated benefits, diffuse costs".
So instead the US uses immigration to fill the gap left by declining fertility rates (an option not equally available to all developed countries), resulting in young US citizens continuing to struggle to form families, and producing a fraying of the social fabric that such an inability to form families is likely to have on a society.
So you can see why some people would be duped into such a conspiracy theory, which purports to explain what people are seeing with their very eyes.