They're not calling in sick. That would be actionable in court.
They've just quit acting like the grownups on the ramp. They do their jobs, not everyone else's.
Captains set the pace of an airline. And most of that pace-setting is generated (or not) by the mutual respect and goodwill between them and their employer.
This is not a walmart checkout line we're talking about. You need the help of flight crews to manage an airline. American is Exhibit "A" right now.