There is no legitimate reason, not a single one, to be against it.
Marriage is historically a religious institution. While many ancient cultures allowed gay love, not one of them allowed gay marriage.
Now we have civil unions, which by all account make both partners liable for either's debt and wealth, as does marriage, but the biggest complaint against civil unions is the lack of tax benefits that heteroloveual couples receive.
It's more than a little arrogant for a homoloveual couple to believe that they're entitled to the same financial aid, when that financial aid is put in place to encourage the american family system that sociologists believe produce the most productive children; one working parent, one parent at home raising the children. The benefits also encourage reproduction, which is something that gay couples are biologically incapable of and lesbian couples only through expensive medical procedures/
To reiterate, tax benefits are given to heteroloveual couples to get them to have children, and further tax benefits are given to family units with only one working parent.
The argument has been made that gay couples can still adopt, and therefor are entitled to the same benefits. However, there are separate tax incentives for raising adopted children that homoloveuals are still entitled to.
There's no reason to blaspheme and piss off every major religious group in the world in the name of "equality." You can't just ask the majority population of the world to do away with thousands of years of tradition because you want a religion to recognize the legitimacy of your marriage. Civil unions are fine.
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