@Nobodyman you have a point that they can't be blamed for what they don't know about. But there's also the whole point being that they are the only ones producing curses hence Geto's whole take on them being weak, instinctually driven monkeys. Which can be a commentary on it's own and a take on a human race but that's not why we are here about.
The thing is the ones that do know of curses actively tried to use the sorcerors as nothing but tools to further their means and they weren't even sorcerors themselves. That's the whole thing with the cult and also how disposable they can be which was why Rika was replaceable.
Geto always had a bit of holier than thou in him and has been shown to dedicate his entire life to Jujutsu. His entire identity was shattered over time because this isn't Berserk's Eclipse and actually makes more sense when you consider it is a myriad of factors that led to him snapping. 1. Rika 2.His junior's death(Haibara was his name?) 3. His whole personality is about doing it for the good of something/a mission and Yuki gives him an opportunity to do the same but this time for something else that he can truly believe in. He changed from being moody/serious to relaxed/carefree isn't exactly a facade and more like he is no longer in inner turmoil between his beliefs and reality.
Him snapping instantly after Rika won't exactly be good writing because he barely knows her (it was only what, 3 days?) and has a more cynical, pragmatic and calm side to him that would have been accepting of that given time if not for the events and experience that happens after.
I don't think it is racism but there's a chance that you can see it as more of how a military soldier that gave most of his life to fight wars and upon his return, realize he is just one of the many tools for war, profiteering, and general human's stupidness(that starts them). And that because he believed strongly to fight for said war that was ultimately meaningless, he and his soldiers got killed. There's a term for that but I can't remember right off the bat. "Was the war really meaningless?" Maybe not, maybe yes but it doesn't matter because he thinks it is meaningless and he thinks that he has a better solution that would priortize the group of people he cares about over the group of people he utterly detest because of how much they can take the peace that he have won for them for granted. You can somewhat apply the logic of humans generating curses the same as how we have so many wars in history that are ultimately caused by human selfishness and stupidity. You would think that people would know that their own ego, selfish desires and stupid notions was the reason for wars and conflicts but you'll also be equally surprised at the justification, ignorance, and the denial of that not being the case. Curses are inherently negative emotions manifested and they will never go away which is the same reason why conflicts will never go away no matter how much we advance as a race. The build-up of that leads to wars that soldiers will have to fight for and try to fix even though they might have nothing to do with the origination of said war. That's a better way to look at Geto's position.
You also have to add in the factor that is Gojo. His best friend that has always stood by "together we are the strongest" but eventually outpaced him, outgrown him and probably no longer thinks that way. Gojo having all that power didn't have a strong moral reason to do what he did either (until Geto left). He was willing to kill people if he had to. I can see how that insecurity of being left behind, of having a best friend who could solve the problem not attempting to do so (and pretty much following orders on a whimsical nature), and all the while having no one to talk to and getting constant identity-crisis level flashbacks (while also having to eat curses, the most negative thing in the world), can further and affirm his need to do what he did.