Why do we criticize people moving up in weight?

I've been reading the Four Kings book about Duran, Leonard, Hearns and Hagler. It's made me think that are we being a bit harsh writing people off before the fight even happens? Duran was a Lightweight, moved up to Welterweight and beat Leonard to a UD, and Leonard was a strong favourite. He did this by getting Leonard to fight his fight. Who's to say with the right mindset, Marquez couldn't do the same? Now i'm not saying JMM is anything like Roberto Duran, but at the same time Floyd Mayweather is certainly no Sugar Ray Leonard. It was all mind games and psychological because as we saw in the rematch, Sugar Ray didn't let the mind games get to him and made Duran quit. Even if JMM loses, it should be a great fight. Some of the greatest fights have come from people moving up in weight. So are we being harsh just for the sake of excuses because we don't want Mayweather to win? I'm more of a JMM fan and love watching him fight, and i believe it will be a great fight, regardless of him winning or losing. Why can't we just enjoy a great fight instead of creating excuses before it has even happened? i totally agree, i dont know the big deal on this weight thing crap, this will be a great fight this weight excuse doesnt really apply in this fight especially on mayweather, mayweather doesnt use his weight to fight his opponents, its his boxing skills that wins his fights, i dont think mayweather got more power than pac either, i think marquez can handle mayweather power because if he can take pac punches, he can also take mayweather punches on speed, marquez already experience one of the fastest boxers so i think he can adjust the only thing that matter to me is if marquez carry his power @ 144 and if marquez changes his style from being a counterpuncher and become the aggressor w/c is bad for him.

It's a shame how Floyd get to bcome the lineal at 147 without fighting ,cotto, Margarito, or Mosley. That was fine cuz it ain't his fault Zab screwed up and let the world title fall into the hands of a journeyman. But he coulda solidified his reign by fightin the top challengers afterwards. He refused, and still refuses. The criticism on this fight ain't directed towards JMM at all.

You misinterpereted my question. I didn't mean criticize him in the way that he shouldn't have moved up, because everyone respects him for that. I actually meant how people have written him off before the fight has even happened and say he has no chance in this fight whatsoever. Also, regardless of the result it has the makings for a good fight, so instead of writing it off why not just enjoy it for the good fight that it should be. I think Mayweather wins by decision but i think JMM will be there all night and pose some problems for him during the fight.

People have been waitin a couple yrs to see Mr boat buyer fight the top challengers at WW. It's frustratin that he absolutely refuses to do it. JMM deserves all the credit in the world for his courage tho.