Unless the baby is in distress, can you refuse an episiotomy to 'prevent tearing' I'd rather take my chances as I've read they cause more pain when healing, increase risk of extending and causing 3rd/4th degree tears. Plus its a guaranteed injury needing stitches whereas you might get lucky and tear much less or not at all. Makes me think 'I'll push you down the stairs myself, to prevent you to falling on your own' is silly logic. Plus, psychologically, having my vagina cut is pretty harrowing! Baby causing tearing is somehow more acceptable 
Do they ask/tell you before doing it? Maybe they do only do it when baby is distress (in which case its OK!)? I don't want to be cut just so its over quicker so the staff can go on their merry way! Tell me they don't do that!