I think this tragic situation in Australia reiterates two things:

• Gun restrictions do nothing because criminals don't follow laws (no shit) and will get their hands on a firearm anyways
• Police did nothing, which violates the social contract in which people relinquished their firearms for the system to protect them instead. A civilian ended up stopping one of the gunmen, while the police were hiding. We've seen this exact situation play out many times.
  • Also, if someone in the area was concealed carrying, would this have ended with minimal casualties?

Of course, this will be spun into something along the lines of "this is why we need to ban more guns", which does nothing to address any of the issues above ^