Perhaps Picard was wrong, but there is no proof to show it. From the way the episode was set up, the paradox weapon was almost guaranteed to work. Picard, who was assimilated by the Borg and should therefore have a decent understanding of the Borg, did not even mention the possibility of the weapon being ineffective
I, more or less, sum that up to the date in which the episode was made.... which was in 1992, which was before the internet and viruses/anti-virus programs existed on a large scale to know how all that works.
However, I'll ignore that aspect and go along with your argument that he'd know if it'd work or not.
Those who say the weapon would not have worked are speculating.
This entire topic is nothing but speculation on both sides..... and of course the effectiveness of this weapon is mere speculation, since it was never used to actually know in the first place, all one can do is
From Picard's point of view, he had a means of ending what Picard himself once said was the closest thing to pure evil once and for all and he didn't take it. In my book, that is the height of incompetence, cowardice, and hypocrisy. Picard is one of my favorite Star Trek captains, but he made the wrong decision in "I Borg".
Perhaps it was the closest thing to pure evil.... but I guess the bigger question that needs to be asked, is could you or I make that decision to commit Genocide if it was our responsibility to make such a decision?
Sure you could say yes, based on your previously explained reasons.... and I suppose right now, I could flip a coin and make a decision with little emotion on it..... but in reality? That's something none of us can truly answer until the moment arrives.
That's a big decision.... a bigger decision then whether or not to get married or have children.... it's a decision that will dictate the fate of an entire species through life or death..... one can not simply make such a decision quickly or take lightly and as proven in this thread and the episode, the answer isn't so simple. Whatever that decision is you make, it is a decision you will have to live with for the rest of your life and it is you who will have to face the consequences of that decision later on.
Picard made his decision after a lot of serious consideration and hearing the views of many he trusted, including the potential victim.... in the end, it could seem as though he made the wrong decision, however since the Borg never did take over the Federation and the Borg threat has ended, it's hard to say with certainty that it was the wrong decision, since in the end, the Federation still won without having to commit Genocide, therefore, it could equally be said that he made the right decision.
The bottom line is that there is no one simple answer to this situation, which was the whole point of the episode, and the point of the question of this thread.
"Was Picard wrong in I,Borg?"
No matter how long we all pick apart the limited information and subjective morals of this question and the episode, there is no one true answer.
It is all left to one's own moral view.
Some here think it was immoral for Picard to not use the Virus.
Some in here think it would have been immoral for Picard to commit Genocide.
That's about as far as the debate can really go, since all this really is is a battle between different moral perspectives.