Data firing at Fajo was a terrible decision. Fajo was unarmed and in no position to threaten Data. Data should have been courtmartialled.
Ahh... The Fajo debate reignites. The man had a 24th century starship at his disposal, & declared that the only way to stop him was to kill him, surrender, or face the consequence of him killing anyone in his way in order to get what he wanted.
Knowing Data as an exceedingly well reasoned individual, we can assume he weighed carefully his options & actions, and made the right choice, for the circumstance. Fajo's mistake was to assume Data can't grow beyond his programming, which we all know is certainly not the case
Riker held onto a secret of mutiny & conspiracy to violate a peace treaty for decades, & wasn't court-martialed. Worf murdered Duras & only got a reprimand
Data was acting in the defense of himself & others while abducted, and was spared the actual consequence of having to kill the guy. Plus, as he may have considered his actions being of a personal nature & not as a Starfleet officer, when Riker asked him about the disruptor discharge, his response of "Perhaps something happened during transport" was a clear cut dose of "mind your own business"