[jzb]

"Aren't they required to obey chain-of-command?"

If an order is legal, yes. Not if an order is illegal. If a superior officer orders a private to shoot unarmed civilians or commit some other war crime, the private is supposed to refuse the order. They are not protected by a "just following orders" defense.

"And doesn't their pay and their family's healthcare depend on them remaining employed?"

Sure. But that does not excuse committing war crimes or otherwise knowingly following illegal orders.

Most of the time, the presumption is that illegal orders will be issued infrequently and by rogue elements in the armed forces -- so disobeying may have unpleasant immediate consequences (say, get thrown in the brig) but long-term they should prevail.

Right now? Well... that's the problem. But if significant numbers of the armed forces refused illegal orders, there's little that the administration can do. Which is why they've been cleaning house to kick out anybody at the top who might push back.