Curiously, Salazar's depiction as a racist seems to be a bit of a post-hoc justification for pureblood racism - wasn't a big part of his justification out of fear that the Muggle parents of Muggleborns would come and try to murder wizards? (Harry Potter's racial politics are fucked at the best of times, but this always seemed a lot more reasonable than it was ever depicted to me.) It's also fuzzy because we hear so little of Salazar's actual words and so much of Tom Riddle/Voldemort and other people being like "what this MEANS is we get to be racist".

My theory is that the basilisk was supposed to be a "hey so we can use this against any rampaging hordes of racists and witch-hunters if they so happen to hear from their kid about the magic school".