Used to work for a state DOT, the region office did an annual picnic. As a joke the maintenance guys would do a "gator roundup". Basically they would save the biggest hunk of tire they picked up in the last month to see who had the biggest. It wasn't unusual to be more than 40lb.
Now imagine a 40lb object hitting you at 60mph. Yeah, it can do a lot of damage.
PS: Retreads were an issue 40yr ago. In the modern world, it's not a big difference compared to new tires. There's a reason truckers are expected to check their tires each morning before heading out.