An interesting point, but I would argue that I was following your dictum and playing within the boundaries.

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?