But can you respect and honor a civil commitment between two people, that agreement forming a family (or if you prefer) a “family-like” unit of society? Take the “m” word out.
But if it's just a "legal contract" (as you and Brian have argued) then why stop with two people? Why not a "civil commitment" among three or more? Why not "honor and respect" a multiple partner arrangement? Polyamorous parties are already arguing under Obergefell that their marriages should be recognized. So far, courts have resisted this. But frankly, under the Kennedy's reasoning, there is no reason not to recognize them.
Brian has stated that "nowhere in the Bible does it say that a marriage is between one man and one woman." If that is the case, then marriage is simply a social construct and ultimately meaningless.
You can't have it both ways. Either Scripture has a definition of marriage which is between one man and one woman for life or it is simply a human construct, e.g. a legal contract. If it's the latter, then marriage has no meaning and there is no reason to limit it in any way.
The Bible never defines marriage between one man and one woman. Repeatedly, it gives us examples of men having more than one wife (actually, the Bible does not have a separate word for "wife." Usually, it uses the word for "woman" with a possessive noun/pronoun: "his woman" = his wife. A man's relationship with women: whether defined as "wife," "slave," or "concubine," was that of possessing (owning) them in some way. All were "human constructs," e.g., socially accepted and respected and protected relationships.
Should another man have sex with someone's wives, slaves, or concubines; it was committing adultery; e.g., a crime against the man who "possessed" those women.
Repeatedly the NT talks of being single. Not only do we have Paul's advice in 1 Corinthians; there is also Jesus' comment that in the resurrection there will be no marriages. At least traditionally, we also have the example of Jesus (and the apostles?) that being single freed them to carry on their itinerate missionary activities without being encumbered by a family.
God's command "to be fruitful and multiply" was not practiced by Jesus, nor, as far as I understand the tradition, by the apostles. We don't have genealogies of the twelve apostles like we do with the twelve sons of Jacob.