I'll separate Gay (man or woman) and Bisexual from Transgenderism (i.e. people suffering from Gender Dysphoria, a documented mental illness).
Going with homosexuality, yes, it would be abnormal. To put it simply (again, being offended by this is like being offended that the sky is blue) living creatures reproduce through sexual intercourse, a male and a female. A same sex couple can't reproduce together, so their sexual attraction to the same gender (don't care snowflakes, gender/sex, same thing) serves no biological purpose.