[rhombus]

I quite understand about Gov't benefits and I do collect them myself (as a married taxpayer). Since I chose to pay fewer taxes does not mean I approve of Gov't involvment in marriage. Nonetheless, I believe the real reason that Gov't is in the marriage business was to protect children and to encourage their care by giving breaks to families and thus encourage that lifestyle.

[babyface00]

Well, your question
I don't see what marriage has to do with the Gov't and/or the Constitution.
can be interpreted in (at least) two ways:

Why is government involved in marriage in the first place?

Why does it matter how marriage is defined from the standpoint of the government and/or Constitution?

I was addressing the second, mostly because now that the benefits are in place making marriage a legal definition and a key to benefits, the historical reasons for the first are rendered largely moot. In other words, even marriage were relegated to religious institutions, or left up to the individual, the fact that federal, state, local and government-regulated private benefits all exist based on that status means that (one of the) the core objection(s) remains.