How do you mean? More blood than a nuclear holocaust? Short of a run-in with a black hole, that doesn't seem possible.
I think that the holocaust from a gradual escalation of tension will be less devastating than the all-out retaliation with everything one side has that will happen when the truth gets out.
I really don't think "the truth getting out" would have that kind of effect. Regardless of who did it or why, the people of earth now know what its like to have cities wiped out in massive explosions, and they want no part of it.
Also, Rorschach didn't have the whole truth yet when he dropped off his journal. He didn't have any information in there one way or another as to what Dr. Manhattan and Ozymandias were really up to.
You have too much faith in humanity. The whole plot is a band-aid, nothing more, placed on top of a deep wound that is infected with necrotizing fasciitis. In ten or twenty years, even if the truth never comes out, people will realize with Dr. Manhatten is nowhere to be found. And, in the meantime, they'll be working on ever more powerful weapons in the hope of building a bomb that's big enough to slay a living god. That arsenal of new and more powerful superweapons is going to be pointed somewhere, once people realize that Dr. Manhatten will probably never return.
Maybe they'll push massive ammounts of funds space colonziation so that not all of their eggs are in one basket. It makes sense when facing a being that could probably wipe out entire planets with a wave of it's arm. And then you've just got interplanetary tensions instead of internetional ones, which will inevitably rise to war.
Maybe they'll encounter alien life but the experience will be tinted by an extreme xenophobia inspired by Veidt's plot and lead to an even worse conflict.
Dr. Manhatten claimed to not be able to change human nature, and perhaps that is true. Is it any likely a mere mortal would be able to do the same?
Two vast and trunkless legs of stone
Stand in the desert. Near them on the sand,
Half sunk, a shatter'd visage lies, whose frown
And wrinkled lip and sneer of cold command
Tell that its sculptor well those passions read
Which yet survive, stamp'd on these lifeless things,
The hand that mock'd them and the heart that fed.
And on the pedestal these words appear:
"My name is Ozymandias, king of kings:
Look on my works, ye Mighty, and despair!"
Nothing beside remains: round the decay
Of that colossal wreck, boundless and bare,
The lone and level sands stretch far away.
Nothing ever ends, certainly not greed, anger, arrogance, and fear, the things that drive all human conflict.
The movie itself suffered from bad pacing. This could have been handled in editing. As a whole, the movie would work better if many of the scenes, particularly the flashbacks, were reordered to produce a more consistant build up.