If you only think about homosexuality, claiming 'natural' should not equate to desirable or advantageous right off the bat either.
In my view neither irrational religious convictions nor demonstrations of what is "natural" alone should define what we decide is right, wrong, desirable or advantageous in modern society. We are intelligent enough (hopefully) to come up with better and more inclusive methods of deciding those things.
However understanding human nature may well guide us as to the extent to which it is possible in practice to construct reasonable laws and moral coes that we, as a species, are actually able to follow.
In my view people should be free to do what they choose as long as they are not harming anyone else. That applies as much to homosexuality as it does to a preference for red wine over white. Regardless of either preference being due to genetic, cultural or a combination of the two reasons.
Outlawing sexual relationships that hurt nobody is going to be a stupid law if the need and desire for mutually satisfying sexual relationships is so ingrained in human nature as to be effectively impossible to nullify on any realistic scale.
Whether homosexuality is due to biology or not does not make it right or wrong. However if homosexuality is so ingrained in human nature as to be inevitable then any morality that excludes homosexual practices would seem to be doomed to conflict, hypocrisy and eventual failure. Thus making it a foolish and bad code of morality.
As a counter example consider rape. If rape is natural does that make it right? A law system and moral code that protects people from being the victims of rape, regadless of how 'natural' or otherwise rape may be found to be is one that places the rights of the innocent individual above the natural urges of the rapist and is a perfectly viable code of morality. It may well not eradicate rape but it should reduce it through stigmatisation and punishment of rapists.
Edited by Straggler, : No reason given.