I think this situation in Nice proves that people need guns to defend themselves. This situation could have gone very differently, but at least the man had the confidence to try to do something to stop the attacks since he had a gun. Guns are not the enemy--it is all about how they are used.
Many believe that an armed public would lead to a reduction in violence crimes. However, many times citizens with guns are still unable to stop violent attacks. Most citizens are not professionally trained at using firearms. Therefore, when an armed citizen confronts a violent attacker, the attacker is often able to overtake the good Samaritan. In short, most armed citizens are not that effective at stopping violence.
While there have been some instances where citizens with revolvers have helped to stop violence, in many cases their actions have done nothing or got more people hurt. The case in Nice is one where they were ineffective. It is even possible, that if someone who was trained for this the attack would have been stopped.
Although in some isolated, exceptional instances a citizen armed with a gun may be of use in preventing a violent tragedy I believe for the most part that they would be more of a liability than an asset. Certainly we should not be relying on an armed citizenry in order to protect and serve.