It's harder to make a bomb than pull a trigger, but it isn't hard to make a bomb. Bombs and other methods of mass attack aren't used because they aren't as viscerally satisfying as gunplay is. How many first person shooters are there? How many "unibomber simulators?" The use of explosives in killing is largely perpetrated by assassins that wish their actions to be ambiguous, while the use of guns in killing is largely perpetrated by amateurs that wish their actions to be legendary. It's not like Harris and Kleibold planted a bunch of bombs and waited; they planted a bunch of bombs and waded in with trenchcoats full of assault weapons. The bombs were icing on the cake, really, an impetus to launch screaming victims into their line of fire. James Holmes could easily have walked into the theater with pressure cooker full of nails and fertilizer and then walked out again but he didn't - he waded in with a shit-ton of guns and started shooting. Bombs? That's the Tsarniev brothers and they wanted to get away with it. They didn't intend to martyr themselves.

Our fascination with guns and shooting is related to personal experience and personal powerlessness. A bomber doesn't have his ego on the line. A mass shooter does.

Somewhere in there lies the solution.