For you non-Americans, let me give you a perspective. Unless you are a member of a violent gang (or SWAT team member), you are unlikely to face a lethal-force situation. You might wind up in something that has a strong potential to become a lethal-force situation a couple times in your life (depending on your lifestyle).
In reality, no laws will create a perfect solution. In the US, heroin and cocain (amongst many others) are illegal, but drug abuse is still a major problem. In the UK, handguns are banned, but stabbings increased (not to mention those past issues of IRA car-bombings). In Mexico, service caliber firearms are mostly banned, but the cartels have lots of full-auto assault rifles (aka, guns from China/Russia/India not Texas).
Whether you support or oppose permissive carry laws, it may not have made any difference here. A gunman surprised people with a firearm and quickly began firing into a large group of people. To shoot him immediately without too much risk to innocents would take skill and luck (at least until people duck).
In this case, the attacker was taken down as soon as his weapon became inefffective. In a crowded situation, that is about the best you can reasonably hope for (unless you have some professionally trained and dedicated people carrying, which would most likely be [retired] spec-ops or protective detail types).