The UCMJ does not differentiate between Privates and heads of departments when it comes to obeying orders.
The horrible advice that those congressfolk gave was clearly directed specifically at privates and spec four. Or maybe some dumb second lieutenant. Nobody else would be foolish enough to follow their advice.
I assure you those congressfolk are not gonna stand up when some service member takes their advice and winds up in Leavenworth.
Just like now,they won't point to a specific illegal order. When that happens, they will say, "oh no, that's not what we meant at all!"
Cowards.