A lot of this is overblown really. A few things:

1. The vast majority of school kids in the US will never deal with an active shooter situation.
2. 43% of school shooters in the US are themselves active students
3. Only 20% of school shooting perpetrators had no affiliation to the school, meaning that ~37% of shooters were former students, teachers, or parents.
4. From 1999 - 2023 there were a total of 131 school shootings, but in 2024 alone there were a reported 332 school shootings.
5. These are some terrible numbers, but statistically it's a rare thing. There are approximately 130,000 K-12 schools in the US and ~75 million students per year. If we assume all schools have the same chance of having a school shooting (they don't) they would have a 0.2% chance that your school will have a shooting that year or 4% chance that in your k-12 years that you would be at a school shooting.

When people talk about school security in the US they often don't consider how litigious and risk adverse the US is. You don't lock doors, build fences, and hire security guards to protect from such a small risk chance, if they actually cared there would be a greater emphasis on mental health. No, they do these things to minimize risk, lower insurance rates, and ward off lawsuits.

The defense writes itself,

"Hey, you can't sue us for your child's trauma, we did everything we reasonably could to ensure that a shooter couldn't get into the school. We built a fence, we locked the doors, we made the kids wear clear plastic book bags, we used a metal detector, we hired a guard, we expelled kids who made threats, and we called the police on people who aren't allowed to be here. If a kid then sneaks a 3D printed plastic gun on site and traumatizes the students it's not the school systems fault."

The US is crazy litigious, especially if a government entity is involved and someone might get a pay day. In my area a high school girl and some similarly aged boys ran away from school while at recess to a forest a mile or two off site. The girl then said she was sexually assaulted by the two boys, called her mom and was picked up and taken to the hospital directly (never came back to the school). The school had reported the girl missing, but only found out about the sexual assault after the mother filed a police report and the police reached out. The school cooperated with the police and reached out to the girl and her mother asking if she was ok or there was anything they could do, but the mother refused to answer their (the schools) phone calls or cooperate with the police. A year later the mother sued the school, the school system, the municipal government, and the police each for several million dollars for allowing her daughter to run away from school and for not protecting her from sexual assault in an offsite location. This lawsuit went on for over a year before the judge dismissed the case.