Why did Noah curse his son?
The key theme in this passage seems to be respect.
Respect and dignity were very important in Old Testament times, especially to the patriarchs of families.
God's Law, given later through Moses, assigned a penalty of death to any child who struck their parent, and of course, he also got the Fifth Commandment to honor ones parents.
Ham may have dishonored his father by describing Noah's condition to his brothers in a disrespectful way.
The other two brothers may have covered Noah without looking at him as a gesture of respect.
Think of what we often do in modern society: if someone stumbles or falls, we often look away (rather than stand there staring at them) as a gesture of respect, to minimize their embarrassment.
Additionally, verse 24 says "When Noah awoke from his wine and found out what his youngest son had done to him..." , which strongly suggests that Ham committed an intentional dishonorable act against Noah, rather than just innocently wandering into his tent and seeing him nude.
While this passage doesn't explicitly mention respect, or the lack of it, we should remember that the early part of Genesis was preserved and transmitted by oral tradition. It wasn't written down until the time of Moses.
Of course, this doesn't mean the passage is inaccurate, but cultural nuances are hard enough to capture in writing, much less in oral tradition.
If instead, the passage focuses only on nudity, it seems unreasonably harsh for Ham and his offspring to be cursed for accidentally viewing Noah's nude body, with no improper intent. Such accidental encounters happen today in every family, and I'm sure they were at least as common then.
