So you are refusing to define a word that you are using to smear Bitcoin XT.
No, it's not a consideration for me since the term altcoin for me in reality is more respectable than XT by far.
I'd say the definition of altcoin covers it because it covers all rule changes that incurred bifurcations in the past as well, this undoubtedly should carry weight when considering the definition of this word. But if I were to choose, I'd pick another word like "altfork" or something like that. Altcoin flatters XT in my opinion.
So now you are defining an altcoin as any rule change that cause bifurcations. Though under this definition if Core hypothetically decreased the blocksize causing a split, under this definition Core would then be an altcoin. Even if Core increases the blocksize in the far future this would also then make Bitcoin Core an altcoin. Surely this example proves that your definition is lacking. Unless you are now taking what I think is the correct position that XT is not an altcoin and you can define it as an "altfork" instead, since I can agree with that definition.
Words work exactly like that, they are defined by authority and popularity, not because some enlightened or self-important person settled the matter. At least not in the general case.
I am shocked by you saying this, do you really believe that we should determine what is truth by applying these logical fallacies? I have studied philosophy and politics for most of my life and I can tell you that this is a terrible way to judge truth from falsehood. I urge you to study some history and to think for your self.