Well, one aspect of your bomb scenario illustrates why outlawing guns is a ridiculous approach; there are plenty of other ways to kill people. We must modify the person, not the weapon they choose to carry out murder with.
The other aspect though is that it is flawed; while not an expert, I'm willing to bet that psychological analysis of these type individuals would reveal that they wish to see their victims suffer before killing themselves. Comparing the suicide bombers in Iraq to mass shootings here is really apples and oranges, we are talking about religious extremists trying to get to heaven and die a martyr vs depressed and upset individuals that want to punish their peers.
You can't honestly expect me to believe that if every kid that was under fire at VT had a handgun on their person and was familiar and practiced with said firearm, that they would not have shot back?
Laws do not protect people, they punish people. Society must change, we can outlaw everything on the planet and we will still find a way to murder people as evidenced by continuing violence in maximum security prisons...no guns for the prisoners nor a lot of other items yet people still die.