Cain and Abel and the atomic bombing of Japan are both straw-man arguments:
Cain and Abel:
Firstly, they're mythical characters (as in, never existed);
Secondly, Cain's inexistant murder didn't cause all the murders in human history.
Indeed, the first murder ever commited, probably, by a man-ape didn't caused all murders in human history.
And the absence of that murder would NOT have stopped
the subsequent ones.
In 'I, Borg', Picard using the paradox would have stopped
the unimaginable horror that followed.
Picard NOT using the paradox program led to the death and suffering of uncounted BILLIONS - an outcome highly predictable for Picard.
The atomic bombing of Japan:
The essential diference between the atomic bombing of Japan and 'I, Hugh' was that in 'I, Hugh', there was no other realistic option
to stop the collective from their ongoing genocide, while in 1945, the atomic bomb gave the allies options
for stopping the war that did not involve the extermination of two cities:
They could have blown up Mount Fuji if they wanted to shock the Japanese into surrendering;
They could have used smaller atomic bombs to wipe out the japanese military bases until Japan surrendered or its military infrastructure was completely demolished.
The allies could build 3 atomic bombs per month; there was no shortage of them.
About the 'logic paradox's chances:
I already addressed this point:
"As for the invasive 'logic paradox' not working - Data/Geordi were sure it would work - and given that their knowledge of the hows and whys of trek tech (even borg tech) vastly surpasses what we posters know (for example, they, too, know the borg adapt and, unlike us, they know much about how the borg do this magic trick), the chances are this 'logic paradox' would have dismantled the borg hive mind."
The chances the logic paradox had of working were very high.