Both the UK and Australia banned guns.... both had school shootings and said "This can never happen again" guess what... it never happened again.
Guns were banned in the UK in 1997, since then there has not been a school shooting and actually gun crime is very very very low.
Both countries had an amnesty and this worked very well, and within a few short year
At last count there were 130 mass shootings in the USA this year alone. The UK has had 7 since 1996.
So I would say no, liberals are not stupid... they are looking at facts and data from other countries who have banned guns and thinking that the USA could do it too.