I'm not supporter of gays. But if we live in democracy, then ok, let it go - allow gay marriage.
But I'm strongly against that they would able to adopt kids. I try to explain why:
I predict that mostly gays are from western countries. There are still many kids who are growing without parents. If gays would have right to adopt kids, these kids growing in gay family can understand it as normal thing and and they can become to be gays. In mostly European countries more people die than born, so, growing amount of gays can have negative impact for country population in long term. But, it's only my conspiracy theory.
In other case, kids who are growing in gay family can be discriminated by other kids in school.
Not a supporter of gay people? What does that even mean? You don't get along with them?
For OP, the issue originates from religion, being gay is a sin. That sin has found its way into policy and law. There are many things that people don't support, but because we have certain freedoms (varying depending on where you live), that support isn't necessary.
The time hasn't come yet in the world as a whole, but the time will come when people no longer need the permission of an ignorant population to have their freedom.
If gay people aren't harming you in any way, what do you care? You need to control the behaviours and desires of other people? Should other people say which desires you have that are acceptable or not?