Roddenberry's vision is great.
In The Pale Moonlight is great, though not Roddenberry's vision.
If the Romulans found out the truth after the war (Which they had no real way of doing), it's possible they'd declare war, but it wouldn't be out of outrage and anger. It'd be because they wanted to anyway and this gives them a reason, and they would only do it if they thought they could win. Which there's no way they could because the Klingon High Council ended up with an extremely pro-Federation Chancellor.
Just like if the Romulans went to war in The Enemy it wouldn't have been because of the outrage of their dead pilot, it would be because they wanted to go to war and the dead pilot made them look like the victims.
The Dear Doctor comparison is the exact opposite of In The Pale Moonlight. In The Pale Moonlight was, go against principle to save trillions of lives. Dear Doctor was, allow billions of people to die on vague principle, and it was a principle that didn't even make sense.
And I've heard the TNG writers say that the 'No conflict' edict forced them to be more creative, because it prevented them from falling back on normal TV tropes.