Deleting implied relationship doesn't delete implying relationship

Propositional calculus and I disagree with you. :-)

Here's the truth table for 'A implies B':
A = T | B = T | A->B = T
A = T | B = F | A->B = F
A = F | B = T | A->B = T
A = F | B = F | A->B = T

In semi-English: If A is true and B is false, then 'A implies B' is false. In real English: If Roommate is true and Friend is false, then Roommate does not imply friend. At least according to propositional calculus, if Roommate does imply Friend, then you can't be Roommates without also being Friends.

With regards to my example, you're actually claiming that I've configured my options incorrectly, because Roommate does not really imply Friend (at least not in the real world). But, in the microcosm of my little web site, if relationship A does in fact imply relationship B, then relationship A shouldn't exist if relationship B doesn't exist.

Here's an indisputable example: Sibling implies Family Member. If there is no Family Member relationship, then there clearly shouldn't be a Sibling relationship.

If you want to make deleting the implying relationship optional, you could certainly make the point that not everyone who uses your module is a strict logician, and therefore might appreciate a little flexibility. :-) But please do at least give us the option of maintaining the formal semantics of 'imply'.