what if a single woman has a child by any means whatsoever? Then she moves in with her best friend or hooks up with a lesbian lover. That's a marriage to you? Why can't she be served equally well by a civil union?
Whether or not it is marriage to
me is unimportant. (FYI, it is not what I would consider a marriage.)
Assuming the "hooking up" is a long-term commitment, consolidation of resources and so forth on par with your typical "marriage" of today, a civil union would be absolutely fine in the case of your hypothetical lesbian couple with children. Just as a civil union would be fine in the case of a more traditional heterosexual marriage that
is a marriage in my eyes. The civil union should be the joining together of consenting adults. Defining or approving "marriage" doesn't need to be addressed by the government at all. You and I are perfectly capable of shouldering that burden ourselves, eh wot?
You keep saying that a heterosexual union of one male and one female should be legally considered differently than any other long-term relationship. I'm saying that there need be no
legal difference between a heterosexual union of one male and one female and a homosexual union of two females despite the fact that you or I might not consider it to be a marriage. If the membership of any civil union generates or involves children, that civil union should be capable of protecting the interests of those children whether the members of the union are man and wife or two women or two men or whatever else.
Oh, and I don't think that the civil union need address the sexual aspects of the relationship at all. If we changed your hypothetical to the single mom moving in with her single sister and forming a civil union to help raise the kid, I think that would be fine as well.