The problem in this case, has nothing to do with Flintoff's drinking, and everything to do with the timing of Flintoff's drinking. No one criticised Flintoff when he went on an all night bender with the English cricket time after the Ashes was over. Why? Because the job was done. He'd finished his work as a cricketer, so it was time to party.
In this scenario though, his work has only started. And to go out and get smashed a couple of days before what was a must-win game (no matter who the opposition was) was ridiculously unproffessional. I don't care how much of a legend Flintoff is for nearly drowning himself (Ummm, Pasag, how exactly does that work again?), there is a time and a place for partying. The exact same goes for school or work. You never get pissed before a big exam or meeting.
Flintoff is perfectly capable of keeping his "larger than life" persona without doing things like this. What he did, didn't make him look like an iconic sporting hero. It made him look like an alcoholic moron, and the laughing stock of the cricketing world. Hopefully he'll learn from it, and save the celebrations for after the tournament, from now on.