Flintoff doesn't have an addiction to drinking - if he did it wouldn't be selfish, it would be involuntary. He just, like many others, likes a good drinking session from time to time. The middle of a World Cup was a very bad time, of course, but there was no reason to suggest it was going to affect team morale. I presume he wasn't going out with the intention of capsizing a pedalo. If he was, yes, that was extremely poor.
Added to the fact, of course, that even if it did affect team morale, it certainly didn't make likely World Cup contenders into also-rans, as those same players had been rubbish for years before.