Homosexuality could be considered abnormal only from a procreational standpoint, when applied to the whole species -- because every species advances itself through procreation, which homosexuals cannot do.
Should it be wrong, morally abnormal and unaccepted by society? No. People are not like other animals and do not need to act based solely on their primal, animal instincts in order to survive and/or procreate. Every species has homosexual individuals, it's now nature works and is completely normal. The sooner society accepts that, the easier it is for everyone.