Career criminals will always have access to dangerous weapons, and no laws will ever change that. In fact, strict gun control laws run the danger of strengthening criminal organizations by providing a popular product for the black market.
That said, these spree killers almost always obtain their guns legally. Powerful multi-round assault weapons are not necessary for self defense or hunting, and in my opinion don't belong in the hands of the general public. Those who wrote our constitution never envisioned guns capable of shooting seventy people in a matter of seconds. They did envision a world where enough people freely carried arms that if a bad guy got up to something, a citizen would be prepared to take care of the situation. Something needs to be done to honor the spirit of that original thought.
And if these guns can't be banned outright, then perhaps people need to sign away a little of their personal privacy in order to get them. I'm a big defender of personal privacy and other civil rights, but this isn't about sex toys or fanfiction or freedom of expression, it's about saving lives. And not an invasive yet simultaneously ineffective token effort at life-saving, like tormenting airplane passengers with assault-like pat downs when they are forced to travel or lose their livelihoods. Owning an AK-47 is always a choice, not a necessity. Those who need such things in their line of work have already passed psych tests and background checks, because they work for the FBI or the ATF.