Is it better to develop weapons tech for your own in-group, or to risk being on the receiving end of weapons tech that another group developed and against which you can't defend yourself due to your earlier principled stand?
I don't think it's a given that if you don't develop a certain type of weapon it renders you unable to defend yourself against it.
No, but it's a given that if you don't develop weapons tech at all, it renders you unable to defend against weapons that you would otherwise be able to counter.