There is nothing to stop anyone from doing this and no legislation against it either (unlike CAA regs). But I very much doubt if anyone would ever bother to ride thousands of miles every week in all weathers on his moped only to have nothing to show for it at the end of the week except a sore backside and a face full of dead flies.
So the threat would not worry me.
Duck's observation on this quote by Biggles does not gel with me. I think Biggles has inadvertently made the real point with his observation that there is no pleasure in having to flog through bad weather. You would have to be well rewarded for doing it to even consider it.
And whatever the official reasoning, that safety consequence justifies the law for me. I pay for the privilege of flying for pleasure, and if it doesn't look like being a nice experience I save the money for later. Anything that might put me under a commercial, legal or moral obligation to fly would dilute the pleasure motive, and shift the balance towards flying in less congenial and therefore less safe circumstances.