This overlooks that a major reason why future-us won't care is because the issue will be A) settled or B) made irrelevant.
People have less ardent opinions about, I dunno, persistence hunting or blacksmithing or the-concept-of-property-rights-at-all because either one side conclusively won the argument or because it ceased to be a need or bottleneck that people felt it was important to struggle over.
I think it's a good reminder to check whether the thing really doesn't matter, in the moment, but if the reason for not caring in the future is A, this is actually more reason to care now, when there's still a chance to influence things, and if the reason for not caring in the future is B, that's ... not really relevant? If our great-grandchildren won't care about pollution because they have infinite clean energy that doesn't really make it not-matter today.
Some user named Dan L commented on an ACX post:
I found this very powerful when I came across it, and I have been trying to keep it in mind ever since.
(See also: https://en.wikipedia.org/wiki/This_too_shall_pass )