If y'all really want to step back and actually look at this logically, this is just an argument that they are using for the goal, I am assuming to be would be to raise the age of voting to 21. If y'all watched the story they said the bill is to allow concealed carry in the parking lot on school property in the car not actually inside the building or classrooms.
I don't think they should lower the age to buy a pistol to 18 because you gotta be 21 to legally get cigarettes and alcohol. With the prevalence of social media I think folks en masse are regressing and may have worse impulse control due to addictions caused by constantly being online.
A law like this wouldn't increase or decrease school shootings though, I really think lowering the age would cause more shootings in general though because an 18 year old would be more likely to do illegal straw purchases for others since they could be enticed by financial gain. Probably a section of organized criminal groups would pay 18 year olds to buy guns for them and the teens would think they have a legit hustle going and can buy shyt to show off on social media
