I personally believe life is a (personal) journey and everyone should be allowed to marry the person they love regardless of race or sexual orientation.
I suspect the reason why people are against "marriage equality" is because they believe being gay or lesbian is a (choice). Therefore the more widely accepted it becomes for gay and lesbian couples to marry, have children, and publically display affection towards one another... the more (people fear their children) will embrace or choose the gay/lesbian lifestyle.
Another group of people would rather not see gay and lesbian people period. They use religion as their reason for not liking them but the reality is they think it's gross or a form of mental illness. People have always "cherry picked" the bible verses they agree with and ignored those that kept them from living life the way they want to.
As far as I can recall the bible says "judge not lest ye be judged", "love thy neighbor as thyself", and "thy shall not kill". If those verses were followed there would be no such thing as racism, discrimination of any kind, or murders and war.