>They didn't do anything useful before being crushed.

That's your assessment, which doesn't really matter as long as there's still demand for mining ASICs. If that's the case it really is a waste because destroying them will just cause the demand to be satisfied via newly produced ASICs instead

That assumes that demand is constant. Their hope is that frequent images of mining ASICs being steamrolled will reduce demand.

Will it? ASICs seem to be totally legal there (and most other places in the world). The part that was illegal was stealing electricity. "Hoping" that "frequent images of mining ASICs being steamrolled will reduce demand" is wishful thinking at best.