I think Chapman was a stronger and bigger man than to succumb to mental illness and frankly mental illnes is not caused by experience, but biological chemistry within the human brain causing psychological problems. People who have survived horrors in real life (such as the Holocaust) may be affected, but most go onto lead normal lives. Meanwhile people living beautiful priviliged lives under western democracy experience mental illnes and go to mental hospitals. Sometimes it is not society but psychological (and screw Durkheim).
Perhaps Yeerkbane could remove the yeerk, and also the andalites could develop morphing technology so that it can 'reset the DNA' and thus reduce the brain damage and injuries without giving huge numbers of untrustworthy humans morphing technology. If not then George and Co are the most unfortunate people; after all many humans could've benefited from yeerks (illiterate people taught to read and fly spacecraft engineers taught superior yeerk technology thus giving themselves employment oppurtunities)but there would be no benefits to George and Co. Just a life time of mental hospitals and requiring care.
