You mention Syria as an example... how can Syria regime be compared with the USA at all?? The USA is a democracy ... If people disagree with some policy they are free to demonstrate and (more effectively) VOTE.
Then if the government decides to ignore polls and grasp power illegally it will only depend on whether the army is on their side or not, if it is then you as a civilian are fucked (when's the last time you had access to nuclear warheads?), if it isn't then, the army is the "militia" that will restore democracy and simple civilians need not be involved (in terms of weapons and battling that is).
At the time of the founding fathers, the difference in fire-power and scale between what weapons were available to a simple civilian and to the military was nowhere as big as it is today.
Sometimes, legislation needs a little reality check and upgrade.
Indeed no-one knows what will happen in the future, on the other hand we all can see what's happening NOW with guns available and spread in the civilian population.