That’s easy to say when you’ve never been in a similar situation. No one can say for certain how they will react in these situations. Don’t blame the victims
But what do you suggest people do in that situation? Sit there and take it? A number of shooters have been neutralized by brave people who tackled them before they could kill more people. I would say people trapped in a classroom have a better chance to survive by rushing a shooter than crouching down and waiting for the bullet that kills them.