They're not special in that regard. Every time Congress votes down caps on the price of a certain medical drug, or expanding unemployment benefits, or stricter safety standards for industrial waste dumping, or just allocates some funds to advertising Earth Day on TV that could go directly to needle exchanges, that has a predictable, knowable body count, it doesn't take an act of war to cause death. All of this is justified because the primary stated goal of the legislation isn't to kill people. You start caring about collateral damage the whole system by which a large-scale government is run breaks down.

We didn't go into Afghanistan to exact some Hammurabic vengeance against the Afghan people, therefore we're certainly not going to stop because we've killed "enough". Just like any sanctioned legal action, so long as we're not actively maximizing civilian death as part of state policy civilian deaths are unintentional and therefore irrelevant. Sure, in practice it actually does matter, but so long as we're playing pretend that a centralized state authority with global influence is anything short of one long drawn-out mass murder it's not fair to cherrypick which dead civilians you care about, it's an all-or-nothing proposition.