I have no opinion about the threshold, but there are two things to correct in your post:
it is the common view of medical and general science during the century-odd that we have discovered and been able to document radiation and its effects... that no amount is "generally recognized as safe" and standards need to be tightened.
What makes your "common view" any more valid than any other "common view"? Especially given that "generally recognized as safe" is a completely non-scientific quantity. In the end, you need evidence to back up such assertions not alleged consensus of vague groups of people.
He is absolutely right though. It is the common view of the scientific community that no amount of ionizing radiation is safe. This is also the basis of all radiation protection regulation everywhere (ALARA principle). The reason is simple: Ionizing radiation creates DNA damage with a small probability which then causes cancer with a small probability (which has then a certain probability of killing you). So even a single particle has a very small probability of causing cancer. There is a minority of people that believe that there are other effects (e.g. radiation at low doses activates the immune system) which dominate at low doses, but this is a minority view point and the data we have does not support this. From atomic bomb survivors see a linear correspondence between dose and risk down to about 50 mSv. For example, from this it was predictated that CT scans cause cancer with a very low probability and this has recently been confirmed.
so a comprehensive review based on science would move the decimal point to the left, at least to .025 mS/year, and perhaps .0025 mS.
Background levels are around 1 mS/year. So why advocate thresholds more than two orders of magnitude lower than what people normally get in a year? I just don't think science has much to do with your choice of thresholds.
This is a fallacy. The threshold should be set on the estimated benefits of a higher threshold vs the estimated harm from the additional radiation. The background radiation has nothing to with it.