Well then perhaps it's about time this practice was made illegal!
Yes there is a question of degree and sometimes there can be unique occasions where you might agree to self position but not on a regular basis - is this in the spirit of CAP371? Were the rules drawn up with the expectations that crews would self position?
Also as an SLF I would be very unhappy with any crew members state if they had just had to conduct a car journey by road over long distances prior to duty.
Can't see any objection to train travel though - assuming you can get a seat I cant think of a better or safer way to get to your departure point other than flying that is!