First, the Corsairs on Canaria are protected by the NFZ.
Second, the Zoners are paying Corsairs via food and credits to do the defense. The miners you're attacking are supplying Canaria. So you're hurting yourselves by doing it. Also, you just made our point. The Corsairs are getting nothing out of this defense deal. And the only thing Zoners are getting is a bigger problem than they would've had if they hadn't hired Corsairs. Hence, why they (and we) want to abolish the agreement with the Corsairs.
Then you'd be under no obligation to leave those miners alone. Win, win, don't you think, so why argue? Corsairs will still be present in Omega-49, only there will also be other factions that have an RP reason to be there.
Third; If the Zoner Council were to vote to cancel the defense deal with the Corsairs, why shouldn't it be removed? (Removed as in; New news item stating that the Zoners have canceled the deal, not brushing it under the carpet.) It'd be supported by the Zoners. And the person who is paying is the one in charge of a contract.. There isn't really anything Corsairs can do if the Zoners decide they don't want to pay the Corsairs to defend Omega-49 anymore.
Besides, as you said, Corsairs want to pirate the miners. Contract gone and your restrictions are gone.