There exists a genetic basis to homosexuality as well as it being a learned or conditioned behaviour.
Wouldn’t go so far as to say that being gay is a form of mental illness but this naturally occuring anti-natural aspect should not be condemned with prejudice and discrimination as human beings are human beings first before they are gay, straight, bi, white, black, tall, skinny, fat or ugly.
http://www.futureofmankind.co.uk/Billy_Meier/Homosexuality_-_What_is_its_Cause%3F
Homosexuality - a Natural Occurence in Conflict with Nature
Homosexuality is a sexual variation that is occurring naturally, yet is against nature. “Occurring naturally, yet being against nature” here means that it manifests itself through a natural process but cannot serve the law of natural reproduction. It is therefore against nature, or rather, a naturally occurring sexual variation that is against nature. Homosexuality is a variation rooted in genetics, and for this reason it is considered natural. But due to the inability to reproduce, it is categorized as being against nature; hence, homosexuality is called a naturally occurring sexual variation that is against nature. Homosexuality, as a naturally occurring sexual variation that is against nature, could never be classified as unlawful on account of any of the natural-creational laws and directives. It is therefore considered naturally normal - although against nature, precisely because of the impossibility for procreation to occur. Certain genes and their characteristics determine the type of sexual variation, including homosexuality. But genes and their characteristics, in turn, are tiny particles of nature and are thus subject to nature’s laws and directives. This then implies that nothing can be abnormal in the sense of its naturalness, if nature permits, indeed creates it; whereby furthermore it follows that homosexuality is a natural manifestation whose anti-naturalness is simply based on its lack of any possibility for procreation. Furthermore, as homosexuality is a natural manifestation, hence nature-given, it cannot and must not be considered, judged or condemned as degenerate and unnatural, and similarly not as reprehensible, as loathsome, and neither as violating natural or human law. What is termed unnatural and a transgression against nature, however, is homosexuality and bisexuality of a sodomitical, degenerate nature - the sexual gratification with and on animals of any kind. This form of sexual variation namely develops exclusively from human thinking processes and fantasies, through which a person is even able to influence genes and their characteristics. By doing so, an individual can generate a particular corresponding predisposition. This predisposition then amounts to an aberration, an antinaturalness, and a transgression against the laws of nature as described in the following verses on homosexuality in Genesis: