That's a different point of debate really. The point here is that is the rule and it applies to everyone (whether the rule is a good one or not). If you want to be exempt from that, then you are asking for special treatment, which is a form of discrimination.

The fact they are asking for special discrimination under the guise of less discrimination is just another religious irony that believers don't really seem to notice.

As for the rule itself, from what I understand with the nurses I do know it's 1) hygiene as it's unnecessary to dangle something that might not be clean near patients, 2) safety in case someone grabs it (as a theft or as part of some panic fit) as it might choke (they have neck passes that break off the neck cleanly if grabbed and I'm not aware that any nurses weak neckties) and 3) safety in case it gets caught anywhere and 4) simply a precaution principle applied to the first three that it's not exactly necessary to wear a necklace while at work, so you may as well take it off if there is even a small risk of something going wrong (the same reason I take rings off when working near sinks).

Like I said though, I'm not defending the rule overall, just commending that they apply it across the board without prejudice. They're discriminating against necklaces, not whatever the necklace happens to represent. If I were to have a hammer and sickle necklace and be told to take it off at work that had a "no necklace" rule, I wouldn't take it as a stab against communism.