Flight and segregation emerge spontaneously in any population where people don't want to be a significant minority, even when they prefer some amount of diversity:
well it appears spontaneously in this game that has a hard set of deterministic rules, but there is no proof that actually this is the cause of demographic flight - just an argument. Probably a correct argument, but I am cursed with the tendency to see the opposition to my beliefs as perhaps true.
Correct, it is not a proof that things like explicit legislation or rampant levels of racism are not the actual cause in some specific instance -- they may be. But it does mean you cannot logically conclude, as many do, that neighborhood segregation is smoking gun proof of continuing rampant racism, or anything else.