I think it was justified. What was NOT justified, was raising his fist towards Baaji.
I think of it this way, like GP stated, this is the third time that something 'bad' happened to Dutta regarding security failure. When they were passing out the clothes and what not to the poor people, AS screamed, and everyone was put ON ALERT, and having something that big, someone stepping into your LIVING ROOM near EVERYONE when his guards and Baaji should have been on alert is a shame. He is frustrated. Here is my psychology class in action for you all. LoL
When some is angry, they tend to become argumentative, which is HEALTHY. It is perfectly ok to argue, however, when that behavior of being arguable turns into aggression, is the issue. For Dutta, he turned aggressive, and someone turns aggressive under factors. For Dutta it was frustration, and goal blocking. When you feel that your goal is being blocked (here Dutta's goal of finding the tapes, and figuring out who that man was was blocked) one tends to become aggressive, and frustration was clearly present.
I think because of how he choose to act during that time, many might point it out to be over the top, yet at the same time, it is a reaction that makes sense. I mean, all the guards, and Baaji were told to be more alert, and yet, this happens. While Dutta was yelling, he mentioned a few members of his family and his pained expression was clearly there when he was about to mention Nakku.
His reaction was out of fear, frustration and just plain unease. Not so much that a guy put a locket around his neck, but that this guy could have stuck a knife through his chest, and turned around and shot his loved ones and left.