No, it really isn't... you've got 3-4 mafia players, you're already in a minority. You found out franconp was an investigator day 3, but you cant be making decisions so rashly and reducing your numbers by 25-33%. You probably don't even know if he's telling the truth (just like us), even if it is a mitigated risk since "well at least he's not on our team". It's ridiculous that you want me to believe anyone would think like that. Especially, someone with your specific ability, you could turn the tide of a day phase at any moment.
It introduces a whole new factor to the game, which is that the longer we choose to keep franconp alive, the higher risk we're going to wake up one day phase and all of a sudden we have to evict two villagers on what will likely be as little evidence as we have now.