Hey muffins. If you want a good excuse for recoil on a laser cannon, how about the pressure created from the super-heated air next to the laser. You don't want it travelling down the barrel and screwing up your shot by knocking the barrel around, so you use a recoil action to pump it out while firing. I think that's a perfectly acceptable answer. It's total BS and I just made it up, but it might keep people from griping.