Why not ban all lethal guns and allow the use of tranquilizer weapons instead?That way you could still subdue a perpetrator and not open yourself up to a manslaughter/murder rap and hopefully stop these nutters getting hold of life ending equipment.
What is a tranquilizer weapon? If you are talking about darts with a tranquilizing compound then that has to be filled on a per target basis because what would take down a 180 pound man would kill a 120 pound female or mildly annoy a 300 pound male.
If you are thinking of a taser or stun gun then those can kill people with medical conditions (yea looking at person try to guess who has a heart defect) or can kill the young or old. With people on drugs the taser might do nothing or it might kill them. There are some people (a very small number) who can just
. Things like heavy clothing or body armor also reduce effectiveness.
If we are talking about blinding laser weapons there have been countermeasures to them for decades.
Until we get Phasers a projectile at a high velocity is still the most effective weapon out there. (and if we do get Phasers the lethal ability of them are quite impressive).