It's very simple to me.
The government should not be in the marriage business. Have civil unions recognized between consenting adults so that no one is being denied the benefit of laws.
As for churches, they should make the call whether they want to sanction gay marriages. If they do, I will not be attending because I believe it violates very clear biblical doctrine. For the same reason I would not attend a church that preached stealing, lying, and adultery were permissible.
I would also not attend a church that shunned or prohibited attendance by someone who had participated in homosexual sex. Just like I would not attend a church that shunned or prohibited attendance by thieves, liars, or adulterers.
I have attended church since I was born 36 years ago. Church of Christ and Baptist. I cannot recall ever hearing a sermon on homosexuality. Most churches aren't spending their time or money on the issue.