Not sure I would encourage head first, other than diving back into a base. For those that have the "X" factor and adopt it on their own, I would help with technique.
Personally, I have broken a leg sliding hard into 3rd (ahh, the old days), broken fingers and my nose sliding head first (ugh, shinguards + testosterone), but almost broke my neck on a hard awkward head first landing steaming into 3rd once (fear of god is putting it mildly). Pete "Charlie Hustle" Rose was my hero for base running growing up playing baseball in the late 1970's.
I would still go in head first today probably at times, at my own choosing and risk, but would be hesitant about teacing it to non-scholaship youth/amateurs as a competitive technique .... other than diving back to bases where an aggressive slap in the face is likely the worst penalty.