Misplaced morality is almost a trademark of TNG.
Of course Picard was wrong. The Borg aren't a race of sentient beings -- they're zombies! Sure, it'd be nice if you could reverse the zombification process and restore everyone to life, but if you see several billion zombies massing you don't hesitate to wipe them out. If you can capture one and save it you will, but you don't risk the lives of your entire species for a one in a thousand chance of saving the enemy. An enemy, I need not remind you, that is trying to exterminate your race and countless others.
I couldn't have said better.