I've seen research that identifies mtb as having the least environmental impact, compared to dobbins and walkers. Makes sense as a high-volume, low pressure tyre will spread weight far better than a hard edge of a boot heel. I'd speculate that people like this are simply used to footfall erosion and see it as normal, while tyre erosion looks different and is therefore wrong.
It's also well known that walkers cause significant erosion of existing paths by walking around puddles and making paths wider, while we ride (wheelie) through them. I was quite amused by his point regarding how some cyclists had ruined a 'nice little path' that wasn't even a PROW (but it's still okay to walk on it).
As for cyclists looking down and not 'enjoying the countryside', it should be pointed out that I get to see considerably more of the countryside than if I was walking, as I cover so much ground.
I did try and comment on his blog, but could't find how.
Silly old bugger.