The bishops of the world should tell us wht to do when it is within their realm of expertise. They have no expertise whatsoever in the matter of regulating weapons, as is obvious from the comments they made.
They would have been far, far ahead if they had stated that the US needs to get on the issue of treating mental illness, and those who have mental problems which may lead to violence (including suicide) need to be identified and treated, and potentially possibly prevented from purchase or ownership of weapons.
Violence is a moral issue - and so is other crime.
The bishops my have a moral issue with violence and crime, but that does not equate with any expertise whatsoever in regards to weapons.
In jurisdiction after jurisdiction where Concealed Carry is permitted, crime statistics go down.
There has not been a mass shooting (with the possible exception of the Major in Texas who killed a number of military) where there has not been evidence of serious mental disturbance/illness. One does not, in their right mind, go about killing children, or opening fire on a large crowd.