It was thought that humans caused the quickening that lead to them becoming mortal. We also had Gaider saying that the Dalish seemed to live longer the more generations they stayed away from humans.
That's what makes it racist. The Dalish had no evidence for this (now known to be false) belief, apart from spurious correlation (and an insidious fraudster in Zathrian). If you're going to believe incredibly racist things without any evidence, then... yeah, you're a racist. If your entire culture is based around a super racist idea without any credible factual support, you've got a pretty racist culture.
Of course you don't - you also think the Dalish are racist because the developers decided that the children of humans and elves are human, even though it makes absolutely no sense to blame the Dalish for how the developers decided to establish the lore.
No. We have this debate every time. I think anyone who advocates for a moral duty to breed a certain way to preserve racial purity is a racist, because they're obviously doing it for racist reasons. This is quite literally what white supremacists believe IRL - that the white "race" is being diluted. Every elf has the right to determine - for themselves - whether they think the identity of being an elf, culturally or racially, has any value worth preserving in the future. Anyone who advocates for a moral duty to interbreed is just advocating for racism.
There's no Dalish view on this as far as I know - it would certainly be racist if they thought that elves had a moral imperative to breed more elves, but there's no evidence they believe that sort of nonsense (see e.g. Merrill). The only time you and I talked about this as far as I can recall is in the context of the Dales closing their border to maintain a racially pure utopia, which is obviously racist.
It's more racist to think that humans caused the quickening than it is to think that elves are "less than people" (as Duncan said of human bigotry against elves)?
Yeah. Because the Dalish also believe that too, on top of this extra super racist stuff. From the codex Entry Arlathan: Part Two (in-setting, an excerpt from "The Fall of Arlathan, as told by Gisharel, Keeper of the Ralaferin clan of the Dalish elves"):
Whatever the case, Arlathan had fallen to the very humans our people had once considered mere pests. It is said that the Tevinter magisters used their great destructive power to force the very ground to swallow Arlathan whole, destroying eons of collected knowledge, culture, and art. The whole of elven lore left only to memory.