If basically all jobs enrich the ruling class, then that isn't what makes working for defense contacters evil. There are many different jobs people can have, so building devices that kill impoverished children is a choice. It's class reductionism to think that the only problem a job can cause is working for oligarchs.

There will always be plenty of jobs getting basic necessities to people, regardless of economic system. Hell, as societies becomes more peaceful and prosperous, there are probably even more jobs feeding people as food becomes more about living than surviving. On the other hand, weapons only exist to kill, and that industry has more opportunities the more fucked up the system is.

If you want to claim weapons can be used for liberation, consider that most weapons created by that industry are funded for imperialist purposes. Most of those weapons only end up in the hands of those fighting for liberation because it benefits their rivals. Most arms are used against those fighting for freedom, and many of those fights only start to make those very manufacturers richer.

It's not like cops are on our side simply for doing labor for oligarchs. If they are class traitors for enacting violence on behalf of the capitalist state, then those who arm them are as well.