They were wrong, and should have known better.
So - they were wrong because you say so.
I guess this is part of your - I don't care about the facts, I'm in my 'see no evil, hear no evil, speak no evil' mode.
Just remember - Picard made his decision being convinced the paradox will work - in other words, he CHOOSE to sacrifice BILLIONS UPON BILLIONS just so that he can delude himself that he's morally spotless.
That was his INTENT - whether the paradox would objectively have worked or not is irrelevant on this subjective level.
Of course, in reality, his bodycount surpassed that of any monster from our history.
All the horrors that permeate our history? They pale by comparison to what Picard choose to allow to happen due to his fanaticism.
No ammount of self-righteous speeches will wash away the river of blood that stains Picard's hands.