I believe the historical reason for the use of shiktza and sheigetz was not to insult non-Jews (it’s actually a pretty pathetic insult if you’re past pre-school), but rather to reinforce to the Jews that they should not intermarry, etc. with non-Jews.
It’s somewhat like if you’re on a diet and you pass a bakery. To avoid the temptation of breaking your diet, you tell yourself the bakery’s products are poison or something like that. Are they really poison? Obviously not. But if it helps you avoid it, then it’s a tactic.