What i dont understand about america?

how can it be justified to have guns in america literally not a year goes by when there is one of these m shootings at a school , are people only getting this idea from the first person to do it? why not ban guns like here in britain , where there is gun crime but it is not anywhere near as bad or does it go near to the extremity of m killings at schools anyway point is who thinks america should ban guns!? me for a start.