If leftist agitators do succeed in provoking another Kent State, the shooters this time around are more likely to be private citizens than soldiers or cops. This would add a new and unpredictable dimension to the response, one the lefties and their allies are completely unprepared to confront---it is just not part of their script since it did not happen during Vietnam protests.
9-11 and the physical presence of foreign enemies in this country bring the war home to Americans in ways the VC and NVA never did.
This might happen in response to, say, vandalism of private property by a mob (as we saw many times during anti-WTO riots) or a mob attack on an outnumbered counter-demonstrator or soldier. In these situations, one shot can easily lead to a massacre.
Which leads to civil war and the possible imposition of matrial law? I don't know, but it don't sound good for anybody, especially those who would like to abide by the law.