I am sure a lot of what you say is true. I know I hate it when the characters are played with in ways I find capricious, regardless of whether or not Gus or his parents are involved.
However, it bothers me a little bit more, and feels more political in nature, when it's this particular problem... the desire to make their ovaries tingle at their daddy!Brian fantasties at the expense of the family created by Melanie and Lindsay for their children and with each other.
I am less bothered by fics that have Mel and Lindsay die than I am with fics that make them bad parents. :(