Civil unions are of the title of a legal agreement same sex couples can gain in many countries of the world that give them a few rights that married couples get. It is an attempt at compromise between liberals who know that gay people deserve full equality and bigoted Conservatives who think that gays don't deserve civil rights and should be cast out of society.
The problem is, compromising with conservatives still does harm. When two men or women are in a civil union everyone including homophobic employers know they are gay. Civil unions may be better then nothing at all, but a country or US state that has civil unions is still treating gay people as inferior to straight people, which as we all know is disgusting and wrong.