That is spoken purely from the instructor liability point of view. Would you after teaching that your provided training is not adaquate to engage in overhead environments give a student thier OW temp card and then say lets go penatrate something and do a little deco because your limitations do not apply outside the training environment.
Here is a logic lesson for you. Please read it carefully.
You seem to think there are only two choices--either I tell students that they must dive like students forever, or I tell them to go out and commit suicide. What I do is explain that there is a lot of different diving out there, and they need to make good choices as to their ability to go forward with something new. I give examples. The course mentioned above, for example, provide guidelines for he various levels of difficulty and danger for overhead environments. It does not tell them to plow headlong into caves.
You might find what follows insulting, but it is not intended to be so. Please read it careful and find the intent.
One of the most powerful books I ever read was Leading Minds: An Anatomy of Leadership, by Howard Gardner. He analyzes people who were effective and ineffective leaders to determine why, and the key is effective communication. In a diverse society, he determines, the key to success is communicating effectively with one specific segment of the population, the segment that too many potentially great leaders fail to address at their level. In fact, they ignore them. These are people whose world outlooks and modes of thinking are still frozen at what child development specialist Piaget said was characteristic of the 5 year old mind. These people think in terms of black and white, right and wrong, good guys and evil doers. When they hear people talk about shades of gray and complications, it sounds like lying to them. In fact, you do have to lie to them to be effective. You cannot admit that a situation is complicated and has many facets--you have to pretend there is a right side and a wrong side, and you are on the right side. These people respond to shouted slogans and bright lines of demarcation, but they cannot even see anything in between.
The argument you just made is characteristic of such thinking. I don't believe you are such a thinker, but that is how you just came across. If you can conceive of a situation in which well informed people look at the pros and cons of a situation in diving and then make a decision, then we can talk. If you think there is either a right or a wrong in major categories and people must be told which is which in every case, then we have nothing to discuss.