Why is gun control so overblown in the U.S.?

Why is it that there are so many restrictions on guns (especially cl 3 weapons in the U.S.). Don't people realize that if someone wants to terrorize their fellow human beings, they can find other ways to do it? Just look at the Oklahoma city bombing and 9/11. Why would a terrorist waste time with a machine gun (and kill around 20 people) when he could use a powerful explosive and kill a lot more?