I have a feeling this is just a negotiation tactic leveraging public sentiment rather than a stance based on morality.

I am convinced that Amodei's "morality" is purely performative, and cynically employed as a marketing tactic. Time will tell, but most people will forget his lies.

These are literally words. The DoW could still easily exploit these platforms, and nothing Anthropic has done can prevent it, other than saying (publicly), "we disagree."

Is it morality or is it recognizing that providing the brain of autonomous weapons has a non-zero chance of ending up with him on trial in The Hague?

It's not so clear the company is actually on the line. They can compel Anthropic to do what they are not willing to do, maybe, this is not the final act. The government needs to respond, to which Anthropic will need to respond, courts may become involved at that point, depending on if Anthropic acquiesces at that point or not. Make a prominent statement against while in the news cycle, let the rest unfold under less media attention.