Yes. And Nechayev was correct. IMO, the blood of everyone killed by the Borg after that incident is (at least in part) on Picard's hands.
And someone just said we didn't really know if it would have worked or not anyway...so? What if it had? You are right; the blood of everyone who died due to the borg COULD INDEED..be rested at picard's feet.
Given the length of his career it is likely that Picard already had the blood of thousands on his hands, everything that happens under his command is on his hands.
The blood of millions of Germans is on the hands of the allies, that does not mean fighting WW2 to a conclusion was wrong. The blood of thousands of Afghans and Iraqis is on the hands of those who launched those respective wars, again it does not inherently mean the decision was wrong.
THere are thousands of examples where all choices are bad. That is why you NEED people of intelligence and moral character like Picard in charge of the Enterprise rather than letting the computer run it. He has to weigh these choices and make a decision.
I for one think he was probably right - as others have pointed out the Borg would likely respond badly to attempted genocide, and if it worked he would kill billions of Borg - hardly a very "starfleet" thing to do.