Which is, of course, not always the case. But that is, in fact, also the whole point A language does, necessarily, have to "make sense". If it doesn't, you can't use it to discuss anything. Let's just look at the present case: Ususally, you would have relatively clearly defined words like sex & gender, you have male & female, obviously referring to biology, you have hermaphodites for very special cases & you have sexual behavior to discuss whether someone is heterosexual, homosexual, transgender etc. It's all very neat and clean, if you want to talk about how good looking that man over there is it's no problem, if you want to talk about hermaphodites, it's also clear, if you want to talk about transsexual behavior it's also fine. Now, let's change the basic definition of some of those words. Let's simply change sex & gender to refer to sexual behavior instead of (biological) sex. Now, if you want to talk with me about "how good looking that man over there is", I don't know anymore whether you mean an actual (biological) man, or maybe a woman. If you talk about "gender differences" I don't know whether you mean actual differences like pregnancy or only behavior. If you change the meaning of more words, you quickly arrive at a language that can simply not anymore be used to meaningfully discuss anything at all. And then, sorry, I will simply switch to another language that has not been stripped of its meaning. A language might, as you rightfully say, not be completely rational, scientific, logical, but at its very core it needs to be at least a little bit of that to be of any use whatsoever.