1 [sound]: THUD! THUD!
1 Serron: Here comes the Allosaurus! Blasters ready!
2 GM: You can't fire weapons on a spaceship! Any idiot knows that!
3 Serron: Ah, irony.
3 Paris: That's not irony!
4 Serron: He said any idiot knows you can't fire weapons on a spaceship. Everyone else knows that's true. But will it stop us?
4 Paris: Ah. Tragic irony.

It does, of course, depend on what sort of weapons you're talking about. But firing anything capable of breaching the hull is probably not a good idea. Which is a common enough trope in science fiction - and especially roleplaying - that I'm sure it didn't occur to any of you to question it.

As for the irony part, refer to the annotation to #1349 if you need a refresher.

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2016-05-10 Rerun commentary: You can of course make weapons that don't pierce spaceship hulls.

Feel perfectly free to take on that Allosaurus with slingshots and pea shooters.