Also, through a quick and dirty search (I'm not a lawyer and not going to review every law case involving a firearm for possible justifiable defense), the use of alcohol has been used as a means to disregard a person's claim to self-defense in court. If they can use it to disregard a claim to self-defense in using fists and head butting, are you saying it couldn't be used against you when using a firearm?
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The same question in reverse could be asked of you. Do you know for a fact, that the use of alcohol has never been used against a person claiming self-defense?
In the two cases that you posted, the defendants were convicted because the circumstances were found to be not in self-defense warranting deadly force. The defendant being under the influence of alcohol had nothing to do with that finding. Then the defendants attempted to use the fact that they were intoxicated as a defense to being convicted because at the time they mistakenly believed the circumstance did require deadly force to defend themselves. The courts ruled that they could not use voluntary intoxication as a defense to making the mistake.
Now, if you think that at some degree of alcohol consumption you will make a mistake in your ability to determine when deadly force becomes a necessary defense - then you shouldn't drink to that level.