Riginslinger-
If marriages and civil unions were pretty much the same thing, this argument would be pretty trivial. They're not, and it isn't.
Unfortunately a state-granted civil union doesn't convey several of the federally-granted and private industry-granted privileges that marriage does.

In New Jersey, interestingly enough, two homosexuals can establish a civil union--two heteros CAN'T, unless both are over 65 years of age. You figure.