What Caliber For Brickbat?

Weer'd Beard has this whole "Gun Death" meme going in which he illustrates just how hypocritical anti-2A people can be in their political posturing.  In this example, Weer'd notes a common cause of death and injury from people throwing heavy items into highway traffic from overpasses.

This one resonated with me a bit more than usual:

Happened to my Mom ~35 years ago now, driving home from work on an LA area freeway. She was lucky really; she remembered seeing two middle- or high-school boys standing on the overpass as they tossed a concrete block into oncoming traffic – her, as it worked out. They tossed the block just early enough that it hit the hood of Mom’s car (breaking it into chunks) and then the windshield on the rebound, as it were. She lived, but the insurance ended up replacing the car.

The cops were sympathetic enough, and were honest enough to explain just how unable they were to identify which two boys on bicycles might be the one’s actually leaving the scene of the crime. Of course no one was responsible for adding some kind of fencing to the overpass to make this sort of act more difficult – until it happened to someone with the political clout to make it otherwise a couple years later. And then only to some of the overpasses that similar attacks had occurred from.

If terrorists were smarter than bored middle-schoolers, they would organize an attack campaign based upon this precise type of incident in any country they wanted to attack and then use social media to subtly influence people to rage at the “ineffective police protection” and “failed politicians” and the like. Fairly heavy trash items are free for the taking virtually everywhere. Turning empty bottles into fire bombs are only one of many easy, cheap possible embellishments.

Who knew egotistical psychopath YouTube posers would be the preferred enemy?

As Weer'd says, not a gun death so doesn't matter, right?  And of course, none of the examples of this type of attack to date are known to be the result of "terrorism".

OTOH I vaguely remember news stories from the early 80's of "union thugs" tossing bricks in just this fashion into 18 wheelers driving down the interstate for not respecting their declared strike; I'm sure I heard/read stories of drivers shooting at people in retaliation, so my titular question doesn't seem all that far out of the realm of possibility to me.

Doesn't have to be the religiously motivated of course, but at some point I think it pretty likely that someone with an existential grudge is going to decide that being effective is better than being famous, and then we really will be in for it, won't we?  When the daily commute routinely includes brickbats through the windshield, I'm going to go with "whatever caliber is immediately available" being the most common answer proffered in reply myself.