Another case.
Say, I can exactly count the result of game will be:
A: 304
Me: 302
C: 294
I add event giving +14 points to C, +7 to me, and 0 to A.
Result:
Me: 309
C: 308
A: 304
So... C was propped up from third to second place (and the event gave most culture to him, which I knew in advance). Nonetheless, I played this with intent of achieving my own advantage (and even succeeded, with numbers above).
Would that be a fair play, or not?
Similar case - International Tourism pact.
I propose to C, which will gain 4 points per turn, while I gain only 1.
But C is far behind and I do not believe he can reach me... while that 1 point helps me (a bit) vs B, which is closer and has better culture production and I am afraid of him.
This will help me keep the lead (whether enough in the end, or not) - but also will help (possibly decisively) C with overtaking B...
In fact, in multiplayer game, situation where You need to make action in context wider that directly parties of attack/pact/event/whatever arises quite often, and the best action isn't necessarily the one that benefits You most on face value.