I once thought that I would homeschool my kids if I even had any, but with what I know now from my training in psychology, I think it would keep my kids from learning important social lessons and would probably leave them unprepared for life as an adult...but it's just my opinion instead, I chose not to have kids

The schools my children attend keep the doors unlocked during arrival and dismissal. The Jr High has the doors locked at all times when the kidsa re in school and you have to use an intercom system to enter. The elementary school keeps their front door open and unlocked during the school day, but all other doors are locked. All the school systems in town have the ability to "lock down" and no one can enter or exit during that. Thankfully, that has only ever happened at the Jr Hi my son attends once and that was when a man was spotted walking near the school carrying what was thought to be a shotgun. (turned out to be an air rifle or something)
When I was growing up, I don't think the schools were ever locked except at night. I was actually glad that the man with the shotgun, had he been a psychopath going to the school) wouldn't have been able to enter the building at all.