The children of each of them were long since raised.
I am guessing you have never been married- because I don't know how any straight married person could think that their marriage has been 'discredited' because Bob and Bill can marry now also.
Marriage serves lots of purposes. If the couple does have children, then one of the things that marriage does do is provide additional economic security to the children.
Remember- the main reason why children in America are not raised with a mother and a father- is because one- or both- of them has abandoned their children.
Preventing Bob and Bill from marrying doesn't help a single child. But if Bob and Bill have kids, then it hurts their kids if they cannot marry.