Imagine when 60 million people in the U.K. realizes that they could make a bit of money on the side, they just need to mine.
That will royally f**k up our difficulty...
Except most of them won't have or think they have the technical ability, or the hardware, or the funds to acquire hardware.
It's not like the average home desktop can make more than negligible gains except for maybe gaming rigs but those aren't necessarily average.