No, its not.
It is, of course, more desirable from the perspective of people who prefer that style of play that others conform to it, but it is in no way “essential”.
It may be beneficial to mutual enjoyment to have table agreement on metagame issues like this in advance (OTOH, one might do well to recognise the inherent incentive structure toward the metagame approach you decry in games which tend to produce a long, lingering defeat with no reasonable route to victory.)
I wasn't angry at my friend, and I wasn't personally seeking revenge. I was role-playing my cat army, which suddenly had its home city burned down. My cats certainly were seeking revenge.
In real life, facing an enemy who has nothing to lose can be highly dangerous, and creating such a situation is foolhardy. Why should a board game be different? Why play for second, when a more appealing alternate goal suggested itself?
There tend to be three kinds of kingmaking: revenge, social dynamics, and wanting to leave. All of them have something in common: they are done for reasons outside the gamespace. They're violating the boundaries of the game.
Revenge (what you did) is out-of-bounds because it's using the game to win future games rather than playing the current one.
Social dynamics and wanting to leave are out-of-bounds because they're using the game for rewards that have nothing to do with the game.