You are misinformed. There is absolutely a debate about the effects of radiation at very low doses. This is not like Climate Change where there is a scientific consensus. Look at e.g. the 2009 April edition of Radiology, which featured the competing articles,"The Linear No-Threshold Relationship Is Inconsistent with Radiation Biologic and Experimental Data" [1] and "Risks Associated with Low Doses and Low Dose Rates of Ionizing Radiation: Why Linearity May Be (Almost) the Best We Can Do" [2].
There is a "debate" like in all areas where there are big money interests. How much of scientists are on "there's nothing" and how much are on the "there's a debate" side?
Linearity in the observed statistics is absolutely not the same as "beneficial." Even if the statistics gets "fuzzy" for low enough doses who can actually claim the real benefits?
Also: the actual dosages matter. The low enough dosages are something where we simply don't have anything to compare to as "full absence". We get some level of radiation all the time. Even eating a banana gets you a little of the radioactive stuff. And we (as animals) get cancer all the time.
> The low enough dosages are something where we simply don't have anything to compare to as "full absence".
Which is exactly why the Wiki article I originally linked discusses laboratories specifically built to reduce background radiation in order to further this research. (Which is certainly a strange step to take, given that there's apparently no debate.)
No, independently of your claims, these proposed and never performed experiments theoretically could provide insight of how much of the observed mutations occur due to the existing radiation to which we're permanently exposed. We simply never observed organisms under so low radiation as the experiments planned to do.
[1]http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663584/
[2]http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2663578/