You only resolve the outcome of a vote if that is the outcome that "wins".
So for Short Term truce, if the law passes (ie, the majority vote is FOR), then next round, nobody can activate the systems listed (note that it doesn't apply until next round; the current round is still fair game). No penalty for those that vote against it.
If the law is shot down (the majority vote is AGAINST), then anyone who voted AGAINST has to exhaust a planet. Anyone who voted FOR or abstained is not affected.
I like this particular card because if the vote fails, those who voted against it to cause it to fail are penalized. But passing it can be a big liability next round, so it's often the case that players WANT it to fail, so it becomes a game of trying to get others to vote against it, while abstaining yourself - those who vote later can sometimes see what's going on and ride the wave if necessary.
(Also, just as a minor note: If for some reason everyone abstained, leaving 0 votes to 0 votes, the speaker breaks the tie. However, based on previous rulings, this tiebreaking is NOT considered a vote, so in this case the speaker could break they tie by saying "against", and it would fail and NOBODY would suffer the penalty).