Homosexuality is 100% natural.
It would need to be manufactured for it not to be. Just like anything else in life, there are people who don't understand and make assumptions that anybody different to them must be weird, or flawed.
Some of the most wonderful people I know are gay, and to think for a second that they are in some way unnatural is just an ugly notion. There are some proper annoying people in the world who are also gay, such as certain tv personalities, or extremists, but that is simply another indication that folk can be annoying regardless.
It's important to realise the difference also between being in love with somebody of the same sex and simply feeling horny and experimental after one too many beers. Having sex with somebody does not constitute being gay. Being gay is either who you are, or are not, as the case may be.