You are not alone in that view...
Link to referenced study report:
In 1999, the Commonwealth of Virginia tasked the Virginia Department of State Police to study the need for State standards for recapped vehicle tires. The occurrence of tire debris along Virginia’s highways gave rise to the perception that retread truck tires were to blame. The study would determine whether there was any substance to the perception.
The primary conclusion from the Virginia study “revealed that the quality of materials and methods of producing retreaded tires are not major factors in the problem of tire debris along the highways” (Commonwealth of Virginia, 2000). The primary study objective was not proved through the evidence collected and analyzed. Of the tire debris items analyzed, only one case was directly linked to manufacturing error in the retread process.
Another interesting bit of information can be found on page 48, that a survey of unservicable tires that 31% were original with the remainder being retreads (mostly one or two retreads).
The perverse bit is the more times a tire can be retreaded the more likely the road debris is going to be from a retread tire however the overall amount of road debris should drop.