They are easily one of the most harmful classes of medications. Sure, they combat anxiety acutely, but wreck ones cognitive abilities in the process. This has been readily observable for a long time.

Plus, the anxiolytic effect quickly turns into a dependency, as when the withdrawal starts kicking in you're inclined to start having anxiety attacks.

Suppose you want to get off them. Now you have a significant problem. Can't quit cold turkey -- you're likely to have a seizure.