I slow down because at a slow speed a collision is less serious, and the stopping distance is less. And it also makes it easier for the driver to overtake. If there's a layby handy I'll likely stop and let any impatient drivers move on.

I agree trying to punish bad driving by the way you drive is bad driving in itself, and stupis. So is using a horn to tell people off, rather than for it's proper purpose, which is solely to ensure another driver knows you are there in case they've failed to notice. One of the bad consequences of driving badly is that it is in fact likely to provoke others to drive badly.