Two more points that already been made but here they are for your consideration:
1. Why should the government be giving any legal recognition to anyone solely because of their psychologically disturbed sex life?
2. Any legal stuff given by civil unions other than health benefits can be done with other contracts or legal stuff.
Yes, there is, in reality, very little need for civil unions. They serve very little purpose to society or the potential participants. That is the very reason that I said that the interest would dissipate after a period of time. Gay marriage is designed as a wedge issue. Civil unions take away the wedge and the issue at the same time.