IMO, being able to swim is important. Wat, if in the worst case, if u need to dump all ur equipment and swim to the boat in case of emergency.. eg, u lost ur snorkel and mask coz u panic underwater and discover ur BC is taking in water coz u rupture the air bladder?
Honestly, i find that the dive agency that certify divers who are non-swimmers are taking a risk and totally irresponsible.
Divers should know that in all scenerios, they must depend on themselves before relying on others for help. Having buddy system when diving is good but it should not be depended on...
I have seen divers when they surfaced, they realised that their buddy had surfaced earlier coz they ran out of air and had to be escorted up by the dive leader or some other divers.
Also, what if both of you hv the same thinking of relying on each other to help if anything were to happen and when murphy's law strikes, both of u realised that both of u cant swim.. i cant really imagine the consequences..