Why does the use of this talent generate 2 negative (Threat) results for a character’s social skill check? Would you not want to help that character? Should this say “opponent’s social skill check”? Should it generate 2 positive (Advantage) instead?

In fact you are correct with your second assumption “opponent’s social skill check” gets 2 disadvantages.

It's designed to give two threat to someone else's social skill check. You most certainly won't be using this for an ally's skill check! You are correct that you would use it on a character who is rolling against you or your group.

I believe the reason it doesn't say "opponent's skill check" is because you can use it on an ally who's trying to convince you to do something you don't want to do. They are not an opponent, but still a valid target for the talent.