i) Evils are rarely self-contained events. It's hard to think of events, even little incidents, that don't cause a chain of events. Even individual evils have a ripple effect. Preventing the evil would prevent some resultant good down the line. Moreover, preventing one particular evil might mean a worse evil would take its place–either the precipitating evil or the resulting evils.
ii) Even reflecting on an apparently gratuitous evil will affect the thinker who reflects on it. And because the thinker is an agent, whatever impacts him will impact what he does. So even if the evil was gratuitous in itself, it can have a purposeful influence on the thinker. It is only gratuitous if considered in isolation. But the very act of evaluating the evil changes the thinker in subtle ways, which–in turn–changes the world based on what he does, and others do in response to what he does.
That's a bit circular, where reflecting on an otherwise gratuitous event makes it non-gratuitous, but it's true nonetheless.
iii) A critic might object that if we all thought that way, we'd never intervene to advert a foreseeable tragedy. But that misses the point. Whether or not we intervene would depend on how farsighted we are. And in fact, God has prearranged things so that what we do is ultimately for the good.
iv) Whether inscrutability is a "cop-out" depends in part on whether that's simply invoked as a blocking maneuver or face-saving exercise to show that, for all we know, any state of affairs is consistent with a hypothetical God's existence, wisdom, and benevolence, absent positive evidence to that effect. But, of course, inscrutability isn't cited in an evidential vacuum. It presupposes multiple lines of evidence for God's actual existence, wisdom, and benevolence.