I know this was not directed at me, but I think you are looking at things wrong.
One can be a fan of the team and at the very same time have a very negative feeling towards the team. These are not mutually exclusive items. For example maybe they think Jason Garrett needs to be fired (poll showed over 90% of board agreed) so they think the best way for this to happen is for the team to lose as many games as possible.
So you ask why people bother to post if they don't "support the team". Well it can be for any number or reasons. Maybe they have been a fan for years and years and years and they don't like this version of the team. Maybe its the coaching staff, maybe its the players, maybe its Jerry, maybe its something else that they just don't like, but they are still a fan at heart and they still like to discuss their team with other fans, many who may share their viewpoints on what is wrong with the team.