See, I don't understand that reaction to the IOA plan. It was a hell of a lot more cunning and plausible than the plan that SG-1 had. The Replicators would have decimated the Ori fleet and the shutdown command did work. What did the SGC come up with? Find an Ark that appears in Daniels dreams and that a book of scripture makes some vague reference to, that has been lost for millions of years despite heretics searching high and low for it on their own planet? Sounds legit...
But it was still completely reckless to use an enemy like the replicators that proved themselves to be so intelligent, adaptive and resilient. The Replicators nearly destroyed the entire Milky Way Galaxy. The only reason they failed is because SG1 miraculously found an uber powerful Ancient device and was able to use it just in the nick of time. There were many times where the Replicators adapted to SG1's weapons and they were no longer effective.
And, you cannot count on the shutdown code always working. At some point, the Replicators probably would have found a way to rewrite their code. Plus, we know that Replicators are what they eat. If the Replicators "assimilate" Ori tech, who knows how powerful they would have become. The IOA plan would have problem led to the Replicators conquering the entire Ori Galaxy, evolving to a new breed of uber powerful Replicator, and invading the Milky Way Galaxy again, but this stop with no way for SG1 to stop them.
The IOA plan would have been like Sisko in WYLB, using the Borg to conquer the Dominion. You are likely to just replace one powerful enemy with an even more powerful enemy.