Nobody wants to be a nobody who goes to work every day, makes PowerPoints that nobody cares about every day, goes home every day, watches TV every day, and in the end amounts to nothing special, nothing memorable, because there's nothing interesting or unusual in life - just boring stagnant nothingness, no moral framework to guide you to heroic status, day after day until you croak.
It's certainly the case that identity politics meets the same need, which is why adherents are so aggressive and get so emotional when the ideology is attacked. If you aren't religious then how do you know if you're a good person or not? Christianity is at heart a methodology for convincing yourself you're a good person, and getting back on track when you sin. Following Christ's teachings makes you good, and if/when you fall to temptation and don't, you can pray for forgiveness and restore your goodness. Pretty simple.
The concept of original sin gets added on because otherwise there might be people who claim they aren't sinners, and that would annoy those who are taking it seriously and trying to genuinely be better people. It's quicker to argue "in fact we are all sinners due to the crimes of our forefathers" than to drill into that person's life specifically and try to identify specific instances of sinning, which is high effort and likely to upset people. By claiming everyone is tainted by original sin, nobody can opt out of the purifying rituals of praying for forgiveness - probably a good idea for community cohesion.
But if you're not religious and nobody else is, then there's an absence of any philosophical framework to tell you what makes a good person good, vs just a morally ambiguous nothingburger. Unless, of course, you sign up to the tenets of identity politics and feminism, in which case goodness comes from supporting minorities and - if you are a straight white man - admitting to your original sin and going through various highly visible purifying rituals that stand in for praying for forgiveness, like stating you will definitely try to hire and promote more women in future.
In the end the moral needs it all meets is the same. Take away the underlying ideology by pointing out its contradictions and flaws, and people are at risk of losing the feeling of goodness that is so important. So of course they go on the attack.