I didn't talk about casus belli, you're just making stuff up.

Sure, things happen all the time without a war breaking out. But it's not like you can "just kill" or "just attack" without repercussions. That's ridiculous thought. It's similar to saying "what's the reason to have a security guard in the shop, when you can just take a pistol and kill him". Security isn't about having an impenetrable defense; such a thing isn't possible. Anything can be destroyed in the end.

There's always a repercussion for attacking the military, be it diplomatic, economic or a military retaliation.