I'd be worried about debris flung into steeply elliptical orbits, though. It wouldn't take much to do some real damage to sats in higher orbits and once the cascade starts there's not much we can do but wait decades for the worst of it to fall into the atmosphere.
Those steeply elliptical orbits would probably deorbit even quicker since a random impulse that boosts the apogee is likely to lower the perigee even more.
Kessler syndrome is only a threat to satellites that are orbiting within the debris, it's not really a danger if you're only passing through (as a ballistic missile would).