1.) I don't see the point in people putting something other than an MBTI type as their type. Don't shout at the world "I refuse to be categorized!" while being on a forum specifically for that purpose.
Not everyone will find the same purpose for something to be used. There were designers who devised purposes for this website, but they knew that not everyone was going to abide by those. Not everyone who attends a Catholic school is going to be Catholic. Not everyone at a homeless shelter is going to be homeless. Don't tell anyone what it's bad to break some De Facto rule that has nothing to do with forum administration.
Being categorized as part of a collective whole doesn't make you cease to exist as an individual human; just as refusing to categorize yourself as part of a collective doesn't suddenly mean you are truly an individual beyond categorization and above the fact that humans are defined by their interaction with social groups and fill a finite number of roles with regards to said groups.
Humans are only defined by other humans, and since all humans form subjective judgments, they cannot objectively judge other humans. The essential qualities of a human cannot be flawlessly defined. I don't think people think they will "cease to exist" if they are defined. It's quite the opposite. It's more like the definition doesn't properly denote who they are, and no definition ever will. However, we do make judgments about ourselves and others so that society can adjust and treat us a certain way. So it's up to us, as a society, to determine whether our judgments are ethical or conductive to our growth. Is the widespread usage of MBTI conductive to our growth? Does it actually
work in a professional atmosphere? Does it hamper people when they're pigeon-holed? Does it foster people's strengths? What does it do?
As a self-help tool, I think it's utterly useless. It doesn't tell you anything about how to improve your own strengths or weaknesses, because it doesn't clearly qualify your personality like O.C.E.A.N. does. And if it doesn't tell you about your own strengths or weaknesses, how can it tell others about how you should find a niche in life? It just gives you a list of functions, which don't dictate behavior, but rather dictate psychological 'preferences'. There's no way to effectively use this thing. People would be better off taking multiple intelligences tests, or attending self-help seminars if they don't already have a grasp of what they want in life.