I am thinking several things here. One is that I do believe that there is a tendency sometimes to try to simplify the world in order to make it easier to understand and handle. And that there may be anger or confusion when the world (other people) refuse to conform to these ideas or concepts.
But the thing is, people will think for themselves, define themselves, and call themselves what they see fit according to what they think is right. You cannot control them, however neat the world would seem if your could, they keep hopping out of the boxes ;-)
As for the rest, people very often do have to experiment to find themselves, in many ways and with many things. The experiment itself does not define them.
And in the question of titles, I rather see them as rough descriptions. There seems to be an idea on many lists that a dom is a person who has never had a sub thought or vice versa, but in my personal experience during all too many years I have found that this is very rarely so. I do not mean on lists, which tend to conform to unwritten 'rules', but actual people in real life.
I have for example seen women who started as sub change over the years and change to domme completely. They did not define themselves as switches, and did not live it either. They went from a 100% sub to a 100% Domme.
In some cases they started out as subs because they thought that women into bdsm had to be subs, and then found that this is not so. In other cases there were other reasons.
In my younger days, as a sub, I used to have this same feeling, that if a dom showed any kind of inclination to experiment I would loose all respect.
I have learned different now. I can explain it no better than to say that if what is there in that person is what is needed for that particular relationship, then that is what is important. If that domination is there, then it is there whatever else there may be, and that is all that matters.