If consensual homicide exists, why was there a need to place a reprimand on Worf's record for executing Duras?
At the end of the day, an interstellar state could not exist like a current day United States. We're talking about species that have evolved in far different conditions and will have far different values. In TOS, I don't think it was ever intended for the Federation to be a latter-day U.S.
As far as Amok Time
goes... T'Pau even says that the battle is for the possession of the woman T'Pring. And the episode indicates that she doesn't really have a way out legally if Spock wins. Then you add in Ardana from The Cloud Minders
, who were Federation members and essentially treated a mentally-challenged subclass as slaves.
I really think the Federation was suppose to be a loose alliance, probably primarily a defensive alliance not a collection morally like-minded folks.