Stickless, trying running barefoot and heel-striking - it's impossible!
Your heel is the narrowest part of the foot, thus if pressure = force exerted / area; then assuming a constant exerted force, then with a smaller area you are putting more force through your legs.
Have jogged up and down the lounge barefoot, but wouldn't dream of doing it outdoors, would get covered in dog sh*t, small stones, fag packets etc.
Have just ordered my first pair of racing flats, will give them a go, but wouldn't dream of doing 140 in them.