February 8th to 14th is Freedom to Marry Week. As others have already stated, marriage equality is not just about marriage but about equality. If one truly believes that gays are equal to straights, and that same-sex relationships are equal to heterosexual relationships, then there is no good or sane reason not to support marriage equality for gay couples.
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This is also a good time to remind everyone of an excellent documentary on gay marriage by Stephanie Higgins entitled The Gay Marriage Thing. For more information on this film click here.