There's a *big* difference between a script that get's passed around and one that is entrusted to a select few. The former are usually put about by writers who are angling to get their script noticed. The latter usually comes from well known and established writers and are accompanied with NDA agreements and sometimes a guard who takes it back once the person is done with it.
Apparently Tarantino decided to trust someone and got burned. I can't say as I blame him for reacting this way.