If the question that is asked about "homosexuality being heritable" means that it can be passed from generation to generation like a trait. Then the answer is naturally 'no' because in order for 'inheritance' one needs to have heterosexual parents. Without intervention homosexuality should naturally die off. Of course with modern technology that can be overcome. Assuming the idea is that males are selected for their manliness to be specimens this reduces the likelihood or offspring being homosexual, supposing still that sexual orientation is genetic. Either way this question cannot be answered without comparing it with the tendancy to being heritable as much as heterosexuality is, if it is. Only by compaing the dynamics of the two can one assess the full impact.
there was a parallel thread in Health Forum on this topic; please see my posts in that thread for the genetic possibilities of homosexuality (of course those might not be true, but one cannot simply refute the possibility of genes underlying this trait...)