Honestly, I wasn't sure how the game would deal with this.
My expectation was that the Specter fails to deal damage as the player in question can't lose life, so the trigger would not happen.
But I looked into it, and the game does consider the damage succesfully dealt, but the player just doesn't lose life because of it.
So you're right, the Specter trigger would work here and defending player would have to discard a card if the Specter went unblocked.
This is fair, but something like
Stupor would be fine to be legal, and I generally don't like mass bannings of effects unless I have a very good reason to do so.
So most here are okay with banning
Gerrard's Verdict,
Chain of Smog and
Dark Deal?