In 2004, the National Research Council reviewed extensive research and concluded that there was no clear evidence that making it easy for law-abiding people to carry concealed weapons increased or decreased violence. Still, that has not persuaded partisans on either side, and the debate flared again after mass killings like those last July at a theater in nearby Aurora and in December at an elementary school in Newtown, Conn.

Opponents of allowing the carrying of concealed weapons say it increases the risk of accidents, and of ordinary confrontations escalating to lethal force. Supporters say it gives pause to criminals, and a fighting chance to potential victims.

“If you had asked students the morning of the Virginia Tech shooting if they feel safe, I’m almost positive all of them would have said yes, but just a couple of hours later, those students found out that feeling safe is not the same as being safe,” said David Burnett, a spokesman for Students for Concealed Carry, a group that was formed after that shooting and has campaigned to overturn college gun bans in several states, including Colorado. “And smaller crimes are as much a reason for self-defense as spree killings.”

Mr. Burnett, 27, is an emergency medical technician and a nursing student at the University of Kentucky, Lexington, where he leaves a .45-caliber Glock pistol in the glove box of his Toyota because it is prohibited in class. His group, which says it has members on 130 campuses nationwide, sued his university in 2010, and the State Supreme Court ruled that employees and students may leave guns in cars parked on campus. Students for Concealed Carry, which is made up of volunteers and says it has no connection to the National Rifle Association or other gun rights organizations, considered the ruling a partial victory in its larger effort.