If someone is going to kill people anyway...it makes sense to restrict guns to people.
You seem to be arguing we might as well sell automatic guns to people who want to kill people, 'as they will find a way anyway'.
Well, no. If someone is in a car, they are going to crash. If someone has a knife, they are going to get overpowered eventually.
Giving someone an automatic rifle, will allow them to commit a slaughter.
They usually plan this stuff in advance. Of course there are some people who should be (And are.) restricted from buying a gun, but it's still not going to stop mass murderers or criminals. Even Obama said that tougher gun laws and restrictions aren't going to just stop these things, maybe just decrease them a little bit. Also, if you Google Mass killings, there was a guy who killed 86 people with a truck once, waaaaay more than about 99% of our mass shootings. So there are some sensible restrictions, bans tend not to work, though.