Have to agree to an extent with Target. We really don't see a lot of weapons on most of the ships in the show, and they seem to do double duty a lot. B5Wars had an 'intercept' rating on all of its weapons, so that a ship could go defensive if it was under fire.
Like the penguin said above, if the weapons have enough of a charge to damage a ship, they have enough of a charge to seriously affect another pulse passing by them. (We know these weapons aren't a pure energy format as they move slow enough to be tracked and fired upon).
/shrug I guess as I don't see it changing any time soon, but the idea seems to pretty clear, fighters shoot down incoming fire. The fact that we see a fighter unfortunately get in the way of a beam in the show isn't really all the important, because that isn't what the mechanic is representing. The fighter wasn't shooting at the beam, the game mechanic wouldn't allow the flight to interact with the beam and I thought we were basing this off implied or stated uses of fighters rather than show evidence.
That said I did think we saw some interceptor duty in one of the movies...but I don't have them so no way to check.
Ripple