the only fact you have is that the word/phrase has been around for a long time and if you truly believe that alone means your argument has merit, then yeah, you're being ignorant of why this is possibly offensive.
So are you willing to acknowledge that chink is a racial slur? If so, tell me why you're adamantly defending a phrase that could easily be changed without causing any problems?
I don't get you. Why are you so obsessed with that point? Why is it so hard for you to understand that "chink in the armor" has been used, to this day, widely in literary works and even with people who use it to this day when working on armor? "chink" alone is a racist slur, yes. But the use of that word alone and the context for the phrase is completely different, and ridiculously absurd to get offended by.
I mean, English isn't even my first language and I've used that phrase.