I don't get offended if people don't understand why I'm into fish keeping. Hell, I don't truly understand why I'm fascinated staring into a fish tank. All I know is that I get mesmerized when I do stare into my aquariums. I guess for me, and most people here, I suppose fish keeping causes a release of endorphines making us "oh, so happy!"
So, basically.....you get it, or you don't. There's no way to explain or share this adoration, so don't bother explaining or justifying to those who don't "get it". Just tell them it brings you joy and happiness period