Despite Morton’s claims and popular belief that people sort into a binary system of left- or right-brained, looking at brain activity did not support this claim.
Another popular myth bites the dust. The notion that people are dominantly left- or right-brained never had a solid foundation in neuroscience, and now the best evidence we have is convincingly negative.
As myths go, this one is fairly benign, but not completely. Any time our understanding of the world is muddied with simplistic and incorrect notions, there is the potential for mischief. In this case, attempting to pigeonhole with a false binary label can be extremely counterproductive in interpersonal relationships and especially psychology.
Such notions also are sometime applied to education with the belief that children have different learning styles that need to be catered to. This also does not appear to be true.
Labeling people as left or right brained is no better than approaching people according to their astrological sign or blood type, except that it has the patina of neuroscience that may cause some otherwise-rational people to take the idea seriously.