It is impossible to ever know precisely when something bad might occur that might cause civilization as we know it to completely cease to be. This is why it is important to remain prepared for such a moment in order to make sure that you can care for and protect your family should society completely collapse. Military field manuals can be super helpful in a time in which survival is not a certainty. These manuals can help you to keep yourself and your family safe from any bad actors in a time in which the world as we know it has collapsed. If civilization were to collapse, there would be a bunch of people out there who would be trying to take any food or water that you had in your possession, and because they are also trying to survive, they would likely be willing to kill you or your family in order to get these essentials for survival.
Rather than living with the possibility of failing to prepare yourself for the worst possible scenario, it is probably a good idea to make sure that you have all of the tools that you might possibly need in the case of a doomsday scenario. You never know when a natural disaster or some other event might cause society as we know it to completely fall apart, and that is why it is so important to prepare yourself now so that you know that you have all of your bases covered if something that devastating were to ever happen.
I definitely suggest that people own guns and train themselves on how to use them, but having some tactical knowledge is also quite important, and that is why these field manuals can really come in handy. Just hope you never need them.