this is obviously a political stance, rather than one of classification.
Logically, if there is a set separating those who self identify as 100% straight as the only set qualifying as 'straight' ... then there should be the same qualification of only those claiming 100% gay as qualifying as "gay".
That would leave the vast majority claiming some admixture out of both sets....
but it is disingenuous, or plain ignorant, to make being straight an absolute and being gay a widely inclusive gray zone.
Either treat both extremes as extremes... or admit that you have a belief set that anyone professing the slightest degree of bisexuality is "kidding themselves" and is really gay but have not come to grips with it yet ( a popular myth in the gay activist community that seeks to include larger numbers of men on their "team" ). The latter option is actually professing an agenda... so cop to it.
But, if you are going to create sets... then you should apply the same standards to both polar extremes.
(i.e. 50% or more gay is in the gay set, 50% or more straight in the straight set.... OR, a gay, a straight, and a bisexual set)
Bisexuality is not only real... it is by far the closest we come as a species to a "norm".