They have decided that the word bisexual means something other than its meaning
I think this is pretty cynical, and I also think you’re throwing a lot of people under the bus if you believe anyone identifying as pansexual is only doing so to score ideological points in the transgender debate. Maybe the biggest thing pansexuals ans bisexuals have in common is facing erasure.
It’s an interesting thought experiment but words need definitions or we all end up in hyper individual realities and lose all power to communicate effectively.
It’s more than just a thought experiment, it’s an absolutely routine part of humanity. Of course words have definitions, but you can’t deny that these are open to interpretation. There are plenty of examples of words having definitions and yet being applied to completely contradictory scenarios, scenarios which might even be in direct conflict with one another. And then when you have words which serve as labels defining a large group of people, you will get many people within that label profoundly disagreeing with each other in respect of what is and isn’t an acceptable part of that definition.
If words never changed their meanings, if they were never appropriated and never evolved, we wouldn’t have the word ‘gay’ meaning ‘homosexual’. The word ‘n**r’ would only ever be a slur, and not a term that POC have reclaimed to use of themselves in an empowering way. The word ‘sis’ would only literally be a shortened version of ‘sister’ meaning your female sibling instead of a term of endearment used by women of others unrelated to them. These are all words which had definitions but which have evolved into something new. The result hasn’t been a descent into some kind of Pinter style hell-farce where words are meaningless and none of us can relate to one another. It just means we have a new understanding, and a new layer of meaning. This is what language does!
And I’m not saying there is never an agenda behind the evolution of language, because of course there can be and often is. But in this case, to assert as fact that pansexuality only exists because a cabal of former bisexuals are seeking to further trans inclusivity isn’t fair, and isn’t supported by any kind of evidence.