At the end of the episode, even though Data's programming didn't allow him to harm another living being, he most definitely fired that phaser at the villain of the episode (forgot his name) but was beamed up before it could discharged. In essence, Data broke his own programming. This makes me wonder something. Let's say Data had lived for thousands of years without ever having installed an emotion chip. Do you think he would've eventually developed emotions on his own?
That's not accurate. Data has a "strong inhibition" against harming living beings. That's not the same as being unable to.
There's an argument to be made that Data displayed an emotional response many times throughout the series. Firing on Fajo is one example. While Data wasn't as demonstrative as many people would be, I get the impression of sadness for the victim and deep disgust for the killer. If he was motivated solely by the cold truth that Fajo's better of dead than at large, why lie to Riker about it? And when Data visits Fajo to say the precious collection is gone, insisting he's not there to rub it in... well, why is he there? As great as "Brothers" is, I'm not quite happy about the introduction of a quasi-magical emotion chip as an instant gateway to human feelings. But even here, when Data say he won't grieve, Soong knows better.