Such inane arguments as "well if we attack people preemptively, what if other people start attacking us preemptively" are so intellectually bankrupt I find it striking, and thus consider it to call out for explanation. How about this one: the people saying it, deny morality, and hold mechanical pseudo-values. Because the explanation of which preemptions are kosher does not follow a mechanical rule, they find it incomprehensible and so make up a mechanical rule and claim we are using it. Example mechanical rules include: all preemption is cool; no preemption is cool; all preemption that Noam Chomsky says is cool, is cool, and the rest is not; or somesuch.