Are we trying to start a world war three? Citizens becoming vigilantes is not the answer to the problem. If everyone carried weapons, there would be more deaths and homicides on our hands. Innocent people would be splattered for an "oops!" We need to leave it up to the authorities. Let them do their jobs.
Regardless of other arguments for or against citizens being able to carry assault weapons, it does not seem that the Boston bombing proves a need for citizens to carry them.
The initial incident was very sudden and would not have left anyone with the ability or time to react in any meaningful way with the assistance of such weapons (or any others). The use of assault weapons by citizens also would not have helped during the later shootout with the younger of the brothers, as it would have been more likely to put citizens at risk and potentially resulted in the bomber's death before more information could be determined about the incident.
Nobody knew about the bomb until it went off. How will a gun stop that? Shoot the bomb? Even if someone noticed the bomber acting suspicious, you can't just shoot someone because they look suspicious. The bombers were not at the scene when it happened and guns would not have stopped the bombing.
The bombing is irrelevant when is comes to any fire arm discussion never mind semi automatic rifles. All fire arms become useless even those possessed by law enforcement when it comes to a terrorist bombing. It's not an open display of violence until the bomb actually goes off.
They become relevant when someone shows off say a bomb strapped to their body and gives warning they will set it off in the name of what ever cause. Is a citizen any less capable than an officer to neutralize someone in this situation ... No not at all. And then the answer would be any firearm including a semi automatic rifle would be useful to stop potential harm.
Assault weapons are far too destructive to be given to citizens, and it is my belief that allowing citizens to carry such weapons will only make this kind of tragedy more prevalent. The idea that people need assault weapons to defend themselves is ridiculous. Loosening regulations on assault weapons will allow criminals to gain better access to high-damaging weapons and cause more devastation with them.
I do not believe that citizens should carry assault weapons. The Boston bombings just prove that there are some crazy people in this world, no matter what religion. If a person is going to hurt another person, there really isn't much we can do to stop it. If lots of people start carrying guns, then we would just have constant shootings. And most of those people carrying guns would not even know how to use them properly, and that could result in more innocent victims.