It's an interesting and complicated topic. Honestly? I believe that homosexuality is mostly genetically based. Not all BEHAVIOUR is (homosexually) genetically-based, but history has, time and again, achingly displayed the strong 'natural' influence of homosexual feelings. In the face of fierce, and sometimes life-threatening social pressures, we still today have a society that (although largely uncertain of the gay place within itself, perhaps - as indicated - as a result of self-sexual uncertainty or phobia) strives to find a place for this ever fascinating type of person. This strongly indicates to me that homosexuality is, for many, a largely pre-determined (and therefore as best as I can tell, genetic) 'preference'.
Is this 'pre-disposition' the result of a malfunctioning, or 'broken' gene? Modern culture would likely jump to the defence of the pro-gay. But, what is clear is that it is not in the traditionally-viewed interest of self-preservation that you mate with members of your own sex. So arguably, perhaps it is a 'fault of the system'.
I suppose the question that should be asked is to the individual; if you could 'flip your sexual orientation', would you? There are many factors, such as technology (IVF, cell-cloning and adoption agencies), as well as the current state of the individual, that complicate this matter almost infinitely.
Of course, this doesn't even take into account the possibility that it is simply not a matter of 'gay or straight' for what is probably a large section of society. How much the 'greying' of your level of homosexual tendency is culturally influenced, and how much of this is a result of 'pre-disposition' however, is beyond me at this stage. I would speculate that the genetic influence would of course be much lower in this matter, than that of the group of 'compelled gays' discussed earlier.
EDIT: As for addressing the question in the thread title directly; I question whether we are too keen for opinions sometimes. I don't fully understand the mechanics behind homosexuality, and so I can only observe and learn as much as possible. Too many times in history, we have staunchly backed an idea that has later proved to be nonsense, or worse. Of course, if my very existence or significant part of culture was threatened by this issue, I would likely take a stronger stance (not unlike how sections of the religious community have). But luckily, I can merely observe without judgement. It is neither a problem or an 'alternative' lifestyle, but more precisely one of many ways in which people follow their ever-evolving routes to wherever it is we think we're going (fulfilment? Equilibrium? Heaven? Ha! Who knows?).