I have always encouraged thorough, honest communication between partners. But now? Well, this one is an exception. You can discuss the 'what', but never the 'why'. My advice: Don't even try to explain why. Instead use the following as a pattern for any such conversation...
Vanilla: But why do you like to wear rubber lockable shorts over your chastity belt, that's also locked? And why do they have to be black?
Pervert: I can't tell you. I just do.
Vanilla: You're not making this any easier to understand, you know?
Pervert: Okay. Try this for size. What's your favourite colour?
Vanilla: Deep blue. You know that.
Pervert: Yes I know. But now tell me why?
Vanilla: I... I just like things that are deep blue.
Pervert: You're not making it any easier to understand, you know?
Vanilla: You're telling me that you can't tell me, because it's a matter of taste?
Pervert: I guess that's it. I can't tell you why I like the taste of some food, and hate others, that are maybe just as nutritious. I can't tell you why on a lot of things, but more to the point, neither can you.
Vanilla: So how do I get a better understanding?
Pervert: We can talk about the what, then, if there's things that turn you off, tell me.
Vanilla: So my likes and dislikes are taken into account?
...And they lived happily ever after?