I think that is the biggest justification for a ban on guns. If something so dangerous isnt available, it cant be used.
Murders rates from guns are very small in the UK, under 50 per year.
With very tight gun controls and severe sentencing for possession of illegal guns the UK makes it very difficult for anyody to amass an arsenal that could be used for a mass shooting.
Of course there is no quick solution in the US as 265million guns cant be removed overnight