Admiral Shran wrote:
The Borg never stopped being a massive threat to the Federation, and the entire galaxy, until Janeway "genocidally" infected them with the neurolytic pathogen, killed the Borg Queen, blew up the Unicomplex, and destroyed their Transwarp Network.
Again, Janeway did that to save her ship
was under attack. Her response was immediate self-defense, and therefore justified under the rules of war.
If Hugh had been the vanguard of an invasion force which was about to board the Enterprise
and assimilate everyone, then Picard would have been justified in using the 'virus' on him. But there was no immediate danger there. Hugh wasn't even part of the collective. So therefore Picard had no right to commit genocide. There was no threat.