Call it abnormal, but we are talking
about 10-20% of the population being sexually attracted to their own sex. Globally, that is anywhere from 750 million to 1.5 billion people.
How about left handed people (approximately 12% of the world's population, or 900 million); Do you call boxing, pitching, or writing left handed "abnormal?"
And shit eating is evidence of a mental illness, but the professional organizations who study, define, and treat mental illnesses, uniformly do not consider homosexual sex as evidence of a mental illness.