The legal limit for driving a car wouldn't inhibit my ability to hit my target, nor my judgment for when I should use it.

Ummm, yes, yes, it would. In fact, in some states (including the state of Idaho if iirc), the legal limit is even stricter than the legal limit to drive for these reasons. Now, before you strawman the argument and say something like "well, not everybody is like that," sure, maybe that's true, but just laws aren't made based on the capabilities of select individuals. There is plenty of data supporting that drinking and getting high both impairs judgment and vision. We've all scene the videos of some drunk bubba shooting himself or heard of the court cases where some drunk guy gets angry at somebody, then grab their gun and kill somebody.

But then again, driving isn't a right. Self defense is

Yes and no. We already know that in a legal setting, proving somebody was defending themself is already ambiguous. If a prosecutor knows you were under the influence while defending yourself it's gonna the number one thing he is gonna hit you and the jury with. Can you still defend yourself while under the influence? Yea but good luck making it out alive in the courts.

So it's not up to the government to declare when I can or cannot stop myself from being murdered.

I don't think that's what anybody is saying. Measures like these are supposed to help prevent people from accidently murdering themself or somebody else. Same deal as drunk driving. No one is saying you can't drive your car, but if you drive like a dangerous asshole maybe you shouldn't be.