Perhaps this article offers an explanation for why the Left targets marriage:

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The survey also found that the most important “gender” gap is not between male and female voters, but between married women and single women, Mr. Zogby said.

“That gap is enormous — married and single voters live not on different planets, but different solar systems, when it comes to their politics and values,” Mr. Zogby said. “Republicans have a problem with single voters, especially single women. The Democrats’ problem is with married people, especially married women.”
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