I understand the questions that arise but let me pose this: If I were to use my firearm in legal defense while intoxicated, wouldn't I be criminally liable? YES I WOULD! Even if you are a lawful user of a substance, it does not give you the right to use a firearm under its influence. Posession should be legally allowed provided that there is no history of abuse or addiction (I do advocate that multiple DUI's be grounds for denial of a firearm). However you have to make the choice; "Do I want the ability to legally use a firearm in self defense or get high/drunk?" No one is stopping them from defending their life, just not using a firearm to do it. Just as you can not drive a car when intoxicated, you have to find alternative transportation.
For those who decide to take the responsibility to defend their life and those around them by carrying a firearm, the choice is easy.....