Disks are 1 hit kills people. It is just the way it is, they are not cheap, they are not to powerful, and they are meant to kill in one hit. If you cannot dodge it then try some other tactic that works instead of just swooping someone with a disk and then *****ing when you die from it.
As far as blocking a disk, I think it should be implemented only if you are turbo, blocking, and have a much higher PL than the one throwing the disk. BTW Cell didn't block Krillins disk, he was simply to amazed at all the power he had just gained that he wasn't paying any attention to anything.
When an attack is created that is much weaker than some one who is much stronger, the attack may go off but does nothing to the individual. Look at when Nail fought Freeza. Freeza wasn't blocking a thing that Nail threw at him but still Nail couldn't do any damage to him because Freeza's PL was so much higher than Nails.