There is a time and place for words, phrases, or concepts to have clear definitions. For example legal agreements like credit cards or purchase agreements are full of them. Key words have specific meanings, which are usually listed in a declaration of terms. If these are your words and your definitions then that is what we must work with if I am going to do business with you.
One of the reasons contracts must describe how you intend for words to be used is because your definition may deviate from common usage due to Historical context, Social context, Political context, Literary context, Cultural context, Linguistic context, Word origin, Contemporary meaning, and yadada, yadada. Point being that both people and the meaning of words can change, and usually do.
Bloodshot69, you are generally correct when you say that, “A short, ugly, fat person has the "right" to label and identify themselves as a tall, athletic, Brad Pitt look alike, it still won't make it true.” But if he lives long enough, has enough money, and plastic surgeons have enough skill, someday he may achieve those looks. (A stretch I know).
The terms straight, gay and bi have been used by some in this thread as though they were some form of manifest destiny. That is you are born that way, live that way, and die that way. This view does not (and should not) describe the true nature of human beings. Like the poet said, “a man's reach should exceed his grasp, or what's a heaven for? “ ("Andrea del Sarto" by Robert Browning)