On the other hand, violence is generally decreasing in the US, so it's quite possible non-coercive approaches could substantially affect the spree-shooting prob

On the other hand, violence is generally decreasing in the US, so it's quite possible non-coercive approaches could substantially affect the spree-shooting problem. Deeper structural changes would be needed to fix the actual gun violence problem in US which is completely different from the spree shooting problem (they're two separate problems, effectively): the violent crimes committed by illegally kept pistols (straw purchased, stolen, inherited, bought off the books) and is usually closely related to the drug war. It is also a deep inequality issue: the poor and minorities are far more likely to be affected than suburban whites.