I feel like there's something pernicious about saying
"The reason you should care about some bad thing that probably involves another group of people is because of the bad thing that might happen to your own demographic later"
I guess it's because it's so contingent on the person's belief that there is this slippery slope, and if you don't believe that, it implicitly tells you that you're off the hook for caring
And it also reinforces the framing that the only reason to care is self-interest