It seems that some people think that morality works on a numeric points basis - plus fifty points for donating to charity, minus ten points for queue-jumping, etc. - and then assess people or actions based on the perceived total score.
So, mathematical morality. There's three related applications of it that I've seen just in the last week, and they're all enraging and favourable to society's default people.
There seems to be this need to elevate heroes, and to stand by them right or wrong, and to use mathematical morality to justify this.
And they either think "Oh, X has got a score of plus one million, there's no way they'd ever do anything significantly negative" or they think "Oh, X has got a score of plus one million, and they may have done this bad thing, but that's only minus a few thousand, so they're still plenty in credit."
And of course, having convinced themselves that their hero is incapable of wrongdoing, they'll dismiss out of hand, with the most convoluted contortions, the possibility that they might have, or that it matters if they did.
So the people who don't get to be official heroes - and of course being a default person makes it much easier to become one in the eyes of the default-centric world - end up discarded to defend the hero.
I'm/they're not an X-ist
This sort of mathematical morality is also, of course, the source for a lot of the common "not an X-ist" arguments that get passed around. It's slightly more sophisticated than heroic maths - only heroes get to have their total scores aggregated - in that it gives points in various sections.
So, for a white person, "has black friends and is polite to them" gets plus 100 points on the "racist/not a racist" scale (it should just be part of the "meets minimum standards of decent behaviour" score, anyway, but...). Using a racist slur, well, that's only minus 20 points on that scale. They're still at plus 80, so they're not a racist. Incidentally, these scales also have low standards - for white people, anti-racist activist starts at plus one, racist starts at minus ten thousand, everything in between is "not a racist".
Of course, it doesn't work like that. Even the most committed activist is going to slip up sometimes, if they're working in an area where they have at least some privilege. Their high positive score might mean that the initial reaction to them is different - a friendly notice, a starting belief that it was accidental, etc. - than it would be to someone with a history of dragging their privilege around everywhere.
What it doesn't mean is that they can cancel things out. Their previous good work doesn't mean that they don't need to make amends for this one time they slipped up. (They may also need to tell other privileged people who are trying to be helpful by claiming this on their behalf to shut up, while they're at it)
Nor can they cancel out the perception of their mistake by doing other good work later but leaving the mistake unamended for.
Ends justify the means
This mathematical morality also infects actions, by letting the end justify the means. So the goal - winning a victory for their political team and keeping the other side out - is worth plus ten thousand points to them. That means, to some people, that they can do nine thousand or so points worth of negative stuff, that they'd disapprove of if it were someone else (like their opponents) doing it, as means of achieving that end.
Their opponents, of course, aren't allowed to use any. Them winning is minus ten thousand on its own. Any negative things they do on their campaign just put them even more into moral debt.
So we see just about every form of discrimination being used as a tool, from people who are allegedly against it, and who'll try to justify or minimise the collateral harm they're causing, while criticising the other side for doing exactly the same thing for the same reasons.