Forum OpenACS Development: Re: Towards OpenACS 5.9
The argument was that with proper RI operators, someone might enter the DB, delete a class of objects, and wipe out the whole contents.
Where by using "foreign key" without "on delete", manual attempts of this sort would be aborted by the db.
Now, as to why one might delete such things manually, at that time. aD's code was really horrible at cleaning itself up.