I don’t really understand it.
The only risk that I can think of related to e-check in boarding passes is potential manipulation of the boarding pass. If the boarding pass is manipulated anyways (removal of SSSS, etc.) doesn’t it stand to reason that the name on the boarding pass can be modified also to ensure that it matches the ID? I don’t see what double review of ID for e-check in boarding passes ONLY proves.
Lastly, didn’t all the hijackers from 9-11 have government issued IDs?