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If civil unions did give all of the same legal rights as marriages (regarding property laws, taxes, et cetera), would you still want to push for full-fledged marriage? Assuming they are available everywhere, of course.
Also, do you think the government should even have a say in who may or may not be married? It could be said that the government should only recognize marriages, instead of administer them; the latter is a private matter, typically where a church is involved thought there are also the Vegas weddings.