You mean that Data should have given Fajo a chance to activate another trap? You mean that Data should have tried to educate the crew about things that they already knew? Who knows what terrors Fajo had used to break them already.
We should take the episode at its word. Based on everything he knew, Data's only option was to fire. We can also believe that Data computed that conclusion in his positronic brain.
It's also worth pointing out that Fajo was cocky at that moment, because he didn't believe that Data actually would fire. Perhaps a single code word from Fajo would have transported Data back to his prison room. That moment was Data's best opportunity.