He [Noah] drank of the wine and became drunk and lay uncovered in his tent. - Gen 9:21
Noah, the only one who was found to be worth saving from all of humanity was found drunk and knocked out. Whatever his reason for being so, we do not see God punish him other than by exposing his sin to us.
We all have our short comings, to pretend otherwise is folly. But notice how the only one punished here is Ham, who walked in on his father's nakedness and told his brother about it.
Noah's sin cause Ham to sin.
Think about it for a second. Ham, it seems, wasn't really his father's son in character. Rather than cover his father, he instead went outside and told his brothers about it, letting us know that he was a bad apple. But who knows, if he hadn't found his dad naked, he wouldn't have been cursed and thus might have had a chance to live a better life, both him and his descendants. Instead though, he was cursed and so were his children.
Sometimes our own sins and mistakes don't have too bad an impact on us. We might repent and life goes on for us. But those very sins might change someone else's life permanently. Sometimes, the motivation for purity shouldn't be us, it should also be others.