Read it from the eyes of the patient. If they hear their doctor tell them that they have no clue, the patient is going to hear it as "I don't feel like dealing with you right now, go away", especially on a topic so extensively researched and debated. In this case they are the doctor, they should at least have a professional opinion, even if that opinion is "there's probably a safe level, but I have no way to figure it out".

Absent the proper research, it seems to me like avoiding any possible risk would be the wise course of action.

That's absurd. See: http://en.wikipedia.org/wiki/Micromort