WHY
Why should the state allow only a small segment of its population access to that tax payer supported facility and prohibit others from using it?
Without clear and compelling reason, I believe the site should be open to all.
I didn't understand the poster to be suggesting the state limit access. But rather stating that shops/instructors shouldn't take untrained divers there.
Why? Because those who are teachers and leaders have to carefully consider the possible interpretation and results of their actions in ways much more subtle than, "Is this legal or not?"
There are many things which are legal, but yet are not ethical, and many things which are both legal and ethical which may still just not be good ideas. Taking a group of learning students (in any discipline) to a spot where they may be drawn by the siren song of the next steps before they are ready, with mortal consequences, just isn't a good idea.
Your act of bringing them there, in a leadership position, may affect their opinion of whether their own chosen actions beyond what you sanction are reasonable or valid. They may see your taking them there as an implicit statement that they can/should do something.
Even if you tell them otherwise.
I'm not a cave diver. I've only seen the environment at this particular location via YouTube videos. But from what I know about people, I have to agree with Mdax and Capt Jim Wyatt.
It sounds like there are plenty of other areas where one can do non technical training in this area. I ask you -- What do you feel is the benefit gained, in the face of this risk, by taking OW students to this location?