They're really not, at least, not necessarily. "What makes people feel the need to justify [their] own actions?" The fact that, as MKSC points out, he loves a club and up until now has been prepared to shell out spectacular amounts of money, time, and goodwill to follow them. He has, like all of us, continually had to justify his own actions in doing so - to himself and his family/friends, and clearly the camel's back has been broken.
Just "not going" is not going to be enough. As has been demonstrated, someone will fill that space, and nothing will change. People don't write these letters to justify their own actions, they write these letters to try to make a point to others who have not yet made that leap. They have quite clearly already justified those actions to the most important person, themselves. As have you, and others who continue to go, and fair enough. It just seems that you are outrageously dismissive of the internal debate, heartache and genuine stress that goes with making such a decision. It's harder to make a major life change like that than it is to just carry on as before.
Of course, if things change then MKSC will possibly go back, as did Mike to the Knicks etc etc. It's weird that you state that the only thing that will bring change is to "stop going", yet you are effectively castigating those who do just that.