The folks who do believe this are taking the bait, all of it hook, line, and sinker.
Libraries are not hurting sales.
Folks not having enough money to function and flourish in a society that tells them to "pick themselves up by the bootstraps" (at least in the U.S.) is hurting book sales.
If you genuinely believe that libraries negatively impact book sales, I don't even know what to say to you.