All marriages that involve consenting, legal adults should be treated equally under the law. A marriage is merely an agreement between two people about a commitment those people want to share with one another. The government should respect the contracts that willing adults enter into with each other and should treat families with equal respect.
Civil unions lack the same legal, medical and financial rights of traditional marriages. Denying people these rights is very directly saying that they are lesser people, which is a mentality that we're supposed to be well past by this point. Bigotry is the only argument against equal marriage rights for all.
If we are all required to pay taxes and follow the same laws, then all marriages should be treated equally under the law. Marriage is not solely a religious matter. My marriage took place in a courthouse. Everyone should have the right to marry, as my husband and I did, and be recognized as such.
Yes, all marriages are and should be treated equally under the law. No marriage is any more deserving of protection under the law than another. As long as both parties are consenting adults, it should be considered a valid marriage, and treated as such by the government. To do otherwise is unfair and immoral.