You bet it's the business of the govenment to decide what constitutes marriage. Marriage is one of the foundational blocks of civilization. All of the legal ramifications associated with scuttling a key component of what makes a family a family will be rendered moot. If marriage is not between a man and a woman for the sake of raising children then it can be anything the individual wants it to be. This is anarchy and chaos.
Also this will allow tthe left to further indoctrinate children on the evils of judeo-christian upbringing. Once this travesty is established as the law of the land, there will be no stopping the left in crushing traditional values.
This is why it is the business of government to establish what marriage means.