Anderson going up in weight to fight Forest and Irving is very different than GSP going up in weight to fight Anderson - the equivalent fight for Anderson would have been going up to fight Jones, which he was no more interested in doing than GSP was interested in Anderson.
Basically Anderson-Forest was about the same as GSP-Bisping, whereas Anderson-Jones would have been the same as GSP-Anderson. Personally I don't believe for a second that fighters don't go up because of teammates - even brothers (let alone friends) compete against each other in much more prestigious and high paying sports than MMA. Not fighting a teammate I can see. Not going after a belt in their division is just an excuse.
Even for the catchweight, the most important number is cage weight, and at cage time Anderson would have been 10 pounds heavier than GSP unless GSP put on muscle, and that simply takes time for already fit athletes in a sport that requires a fair amount of cardio. I suppose if GSP mainlined (ie used at much higher dosages than could be hidden) steroids he could have gained the weight in half a year, so it would have been possible in Pride, but not in the UFC.
Ultimately, its simply odd to expect GSP to fight Anderson while being smaller in a sport with weight divisions. Get rid of the weight divisions and then it would make sense, though I doubt anyone would be paying much attention to either of them without weight divisions.
GSP in the end did go up, after four years of retirement (and looked incredibly slow and awkward in the fight, as well as very unfit - I wonder if he trained at all in the four years). That's very different than going up while active. His return is completely about money (not blaming him, blaming the UFC for giving him the title fight) - at 38, after four years of sitting on his butt he wouldn't last a round against his former self, and I suspect he knows it.
It simply comes down to one thing for me: either weight divisions serve a purpose or they don't. If they don't GSP should have fought Anderson despite being smaller, but then both of them should have been trying to fight Cain or JDS instead of each other anyway. But if weight divisions serve a purpose, there was no need for either of them to either go up or down to fight in another division. Me, I think they should get rid of weight divisions (combat sports started without them, there are no size divisions in major sports like soccer, football, baseball, basketball, hockey, track and field, swimming, tennis - in fact weight divisions are stupidly artificial). But if you're going to have them, stick to them.
Having weight divisions is simply a very artificial and silly thing. It causes all sorts of problems because of dehydration and missing weight which doesn't exist in 99% of sports. They no more belong in combat sport than they belong in basketball or football or hockey. Yes that gives bigger guys an advantage, but that's true in all contact sports (and most non-contact sports), why shouldn't it be true in MMA?
