Second, the idea that people who are expressing dissatisfaction are tying their "self-worth" to a bunch of kids playing a game represents multiple logical fallacies. Its a classic straw man. It knocks down a (faulty) premise created by the individual making the argument.
Regarding the quoted portion, why would someone get so irrationally angry over a form of entertainment that they have no control over? For many fans I think it is a reflection of self-worth. I feel this myself, even with something as stupid as having a feeling of inferiority if the B1G has a bad bowl season (I mentally explain to myself how stupid this is, but the feeling can still persist).
But I also agree with you that there are others who have different reasons underlying their frustration/anger. Reasons relating to the wonderful irrationality of fandom, and the important role that Hawkeye sports can play in one's social life (connecting to friends, family, etc.).
For me personally, the Hawkeyes are entertainment. When things are going well, I spend time watching, reading about, and discussing the team online, all of which adds to the entertainment value. When I find the Hawkeyes having a substantial negative effect on my mood, I back away. I stop paying so much attention, I definitely stay away from the message boards. Doing these things would not add to the entertainment value, but rather detract from it.
For those that take a different tack, specifically venting on message boards, I would love to see you articulate your reasons. I am sure some of them involve compelling stories of the importance of Hawkeye sports not just as entertainment, but as a thread holding together social fabric across Iowa and beyond.