Of course there is no on/off switch. What I am saying is that flying above 250 knots below 10,000ft is not a statistically significant danger to the aircraft or its occupants in most situations.
Flying near flocks of migratory birds, low over forests in Africa or near thermalling flocks of birds is of course a different story. I just think that saying flying above 250 knots below 10,000ft is rolling the dice is a misleading and not quite correct statement. I see the point though, although I'm happy in most non restricted situations to go blatting along at 290 knots without worrying too much below 10,000ft, in fact it was SOP before the 250 below 10 was introduced to the UK.