Gaining access to the normally-locked flight deck jump seat seems like a pretty big potential flight safety threat to me.

Imagine if you could bring your own water, and drown in it! Horrifying!

Tell you haven't read the article without telling me you haven't read the article.

??? You can bring anything you want in your KCM/CASS luggage, including a water bottle, which is not allowed through the "civilian" checkpoint

Because your luggage is not checked at all. I'm sure that a state level actor could circumvent TSA but an amateur could not, and they pose a huge threat too, see the recent bombing attempt at the Tailor Swift concert or the Trump assassination attempt

Allowing literally anyone to get into any airport and into any locked cockpit without any screening is critical to flight safety. If you can’t immediately see why I’m not sure what to tell you.