I think that logically, it can't be genetic, and those that promote it as a 'genetic disorder' are seeking an easy excuse for the behavior. The only way I can think of for it to be purely genetic, is if it's an abnormality like 'FragileX syndrome' or something, in which case it would amount to 1 case in thousands, rather than 2-3% (or 10%, as the gay lobby falsely claims.....)
Unfortunately, the entire genetic theory has become so politicized, that the true answer will never come out.
IMHO, I think that it's a combination of learned behavior and a chemical imbalance.