Bisexuality isn't as scary as homosexuality to tell, I guess. When a person comes more comfortable with their own sexuality, they will become less affected by what people say about it. I think that is what happens with some people who aren't really bisexual. As for switching on a whim or seemingly every day, I do believe that is an attention thing.
What it really does is annoy people, especially the true homosexual, bisexual, transgender - what ever people who have defended all their lives that it isn't a choice.