I think the other side of the argument goes that (a) the bombings would happen anyway, and (b) bombing is very expensive so nobody actually profits from the insider trading. (The bombs "only" get marginally cheaper.) Thus the only actual effect is the early warning, which is a good thing in this case.

Like if someone managed to figure out a way to make slightly cheaper bombs but with the tradeoff that the cheaper bombs gave a few hours of eary warning to the people being bombed, I think I would prefer you used those bombs.

(There are many other cases where insiders may change the outcome to align with their bet. That is bad if the outcome is bad.)