One alternative is as legitimate as another...right?
And why not? If the very meaning of marriage has been changed to include one 'alternative lifestyle', why not another?
When gay marriage is argued for by activists who want it legalized, they often unfairly compare it to the civil rights struggles of black Americans. If they were able to use that comparison as part of a strategy to have government force others to recognize their lifestyle, then they should have no problem with other alternative lifestyles using their struggle to legitimize their own movement.