Many universities now require "closed" fraternity/sorority parties when alcohol is present through which invitations be distrbuted and guest lists registared. Most all in the name of liablity. And while you don't ask "Are you a Gentleman?" at the door, the member responsible for inviting the non-member is responsible for the guests behavior or well being.

Which does bring up an interesting question, if a guest is acting poorly at a party, what repercussions should fall to the member that has invited the guest?