Should weapons be stock? No, we've already got plenty of other ways to kill Kerbals. Including building missiles.
There used to be a Macey Dean inspired "Naval Battle Club" thread. The ships were all stock, and they made some pretty incredible things. From what I saw of it, a lot of the participants just wanted to test their engineering. The explosions were somewhat of a side effect.
After a while, I think most people who play KSP start trying things the game wasn't built for, just to see how far they can push it. For some, that means building propeller aircraft, or giant amphibious jet rovers, or creating a warp drive out of landing legs, batteries and girders. For others, it means mods.
And for some, it means building a 100 ton armored behemoth that can fly to Jool and launch Separatron-propelled I-beams at other ships.
I'll admit that I have had the urge to blow things up. I installed BD Armory and felt a bit guilty, until I started dodging missiles. Mods can be fun.