If they think it's not brought up in elementary schools, they'd be wrong. Whether you allow them to marry or not, there are gay partners in committed relationships, some of whom raise children. The fact that they are not allowing them to make the commitment doesn't mean that the issue of gay couples won't be brought up in school.
In terms of the whole churches being forced to go against their beliefs, being sued for discrimination etc. - you choose to join a church, and you choose to sign up to its doctrine. No one's going to sue a church for something they believe because they don't have to join that church, or get married in it.
And speaking from a country where gay marriage is allowed (although it is called a civil union, but that's just the same as a heterosexual union), there are churches who are happy to marry homosexual couples and churches that aren't - but no one has been successfully sued for denying them the right to marry in a church which doesn't support heterosexual marriage (in the same way that some churches can refuse to marry unbaptised couples, or couples who do not live or were not born in that church's parish).