i have used slow cookers for years & have never used anything other than the low setting.but then i never read the instruction manuals for anything
!my current cooker has three settings.low,medium & automatic(starts on high then switches to low once the desired cooking temp is reached).in the instruction manual(i did read that bit out of interest) it shows the cooking times for the same ingredients which are shorter the higher the temp setting.so in my opinion the different settings have nothing to do with food safety or the type of food being cooked,merely cooking times.
i think that two more important factors apply to this and,in reality,any other cooking technique:
a) the temperature of the food to be cooked at the outset.i always cook everything(apart from fish,seafood & anything that says"best cooked from frozen")from room temperature.
b) the provenance & husbandry of meat.nowadays meat rearing standards are so high in the uk(thanks largely to our experiences with mad cow & foot & mouth diseases) that it is ok to cook good quality home raised pork pink.
unheard of even a few years ago.
but that's just me!