There's one saying in my country:
"Guns don't kill people, idiots with guns do."

Am I against guns? Yes.

But, more than that, I'm against letting anyone to buy it at any time.
If you look at last few shootings in US schools (by teenagers), you will see that all of them were troubled guys, some of them even had troubles with law not just their personality. Some of them had a record of shooting cats and dogs, mental illnesses, depression, and so on.

Why is it easy for them to buy a gun?

In my country, if you want to buy a gun police has to issue a permission, psychologist too. If you have any mental illness, or troubled behavior, no guns for you...at all.