This is just like any other argument where one moral position is used as support for a legal issue. You have the right to decide your own values and moral beliefs, as long as they do not impinge on the rights of another. So, in effect, you can decide for yourself who you want to be in a relationship with, and what gender you prefer your partner to be. It does not affect those who may choose differently. Denying homosexual couples the same rights afforded heterosexual couples is discrimination based on sexual preference and identity.
Giving a homosexual couple the right to provide insurance benefits for their partner, and to have all of the legal rights that such a legal union provides does not affect those who live a heterosexual lifestyle one iota. It takes absolutely no right of a hetereosexual away.
If you don't want to be involved in a homosexual realtionship, then don't get involved in one. But no one has the right to tell another who their life partner will be. Nor do they have the right to deny the same privilegedes to others that they demand for themselves.
Civil union is a legal concept, not a moral issue. I have the right to decide who I want to spend my life with, who I want to have a legal power of attorney over decisions should I become incapacitated, who is by my side at the time of my death, who I support through the provision of insurance benefits, and whom I turn to for support and companionship throughout my lifetime. And each and every other human being has the right to decide such, as well, irregardless of their sexual preference.
Any couple that manages to maintain a lasting and loving relationship over time is to be congratulated, and it matters not a whit whether it was accomplished by 2 males, 2 females, or a man and a woman. I have a dear friend who was raised by a Lesbian couple that have been together for 40 years. They own a home, have raised a child, have maintained employment, are are fine and respectable people who have done a better job of living a moral lifestyle than many herterosexual couples I know. My best friend is a gay man who is neither promiscuous nor prone to amoral or illegal behavior. He is a respected professional, and contributes in a positive way to society and the betterment of mankind. He is a supportive and loyal friend. He gives me support for my relationship choices, and I do the same for him. He is my friend, and has been for years, because of the strength of his ethics and his good character. The gender of his life partner is not a concern.