Did you read the article? The first evidence it examines is roadway deaths vs speed limit, and the author concludes "there is little correlation". I'm not saying I agree with the article's conclusions, but it's easier to trust someone who shows some evidence than someone who just suggests that evidence which supports their conclusions exists.
I just take 'little correlation of deaths v speed limit' as an argument against speed limits in general. Otherwise, what is the point of raising the issue?
Also, he says:
'10 times as many people die on UK country lanes than on motorways. This furthers our evidence that motorway limits have less effect on deaths than other roads..'
Comparing country roads to motorways? A country road could be one car width or two car widths at best, with vehicles driven, often, erratically in both directions with little warning of obstructions or oncoming traffic.
A motorway is 3 or 4 lanes of vehicles travelling in the same direction with virtually zero chance of anything coming the other way, usually clear visibility and advance warning of obstruction, etc
My memory of years ago is that comparing the survival rates of someone hit at 30mph vs someone hit at 50mph was a part of every driving test. And unless my memory is very wrong, there is an extreme correlation there.