In Colorado Springs, a man went on a shooting rampage last week, indiscriminately killing three people before he died in a shootout with police. Some minutes earlier, a caller to 911 had complained about a man with a rifle. But state law allows firearms to be carried openly, and the call was treated as non-urgent.

Compare this with an incident four days later during which four students in a California college classroom were attacked by a man who was later killed by police. Also horrifying and frightening; but the students had been stabbed, not shot, and all are expected to survive.

There are stark differences between these two incidents of violence, but both prompt the same question: What if?

Imagine if Colorado weren't so permissive in allowing people to openly display guns. Would that 911 operator have recognized the danger more quickly and would lives have been saved?

Similarly, imagine what would have occurred if the attacker at the University of California at Merced had wielded a gun instead of a hunting knife. Would there have been fatalities instead of injuries, and would there have been additional victims before the attacker could be stopped? Indeed, would the construction worker who bravely broke up the attack have been able to do so if a gun were involved and not a knife?

It is impossible to answer such what-ifs with certainty. What is increasingly clear is the illogic in many of the arguments advanced by opponents of sensible regulation of guns. The claim that open-carry laws provide an effective deterrent to would-be attackers and criminals was undermined not only by the events in Colorado Springs but also by the testimony of police chiefs across the country who say such laws place added burdens on law enforcement. It is simple nonsense to liken the damage that can be caused by a knife — or baseball bat or whatever other weapon the gun lobby feebly offers up as an alternative — to the lethal capacities of guns.

Many factors contribute to violence. Investigations into these incidents will provide more information about the men who went on the attack in Colorado (a 33-year-old) and California (an 18-year-old) and specifically whether — as has been the case in so many tragedies — mental illness played a role. What should not get lost in that examination is the difference in damage that was done with a knife. That underscores once again the need for this country to follow the lead of other countries in limiting guns and controlling who has access to them.