You're absolutely right that one should avoid getting himself under the influence of any substance while gambling.
Gambling is something that should be done with a clear mind, in order to allow calculate the risks properly before making your stakes, which isn't mostly possible when you're intoxicated by an alcohol.
Well of course the only exception is if it's consume moderately as you've said, but one thing we must consider is that gambling can easily influence ones current emotions and actions in some way, whether negatively or positively so it's better to completely stay of substances while in the casino.
Gambling not under the influence of alcohol will make us focus more on the bets we play to be able to win from the bets we play. When someone bets and loses of course they will become emotional and if they are under the influence of alcohol it is likely they will riot. and this will certainly be very detrimental to themselves.
It important that gamblers should know this, gambling under influence is never a good idea, they may have to make their set target and see that they work towards it, its not a decision for them to completely stop drinking or taking any other form of addictions they are used to already, but we may have to reevaluate the way things are for the benefits of our own sake, we can drink when we are not gambling and while gambling, we should abstain from getting drunk.
Indeed, it is not very good when someone gambles under the influence of alcohol, because it will be very difficult to be able to focus on the bets we place if we are under the influence of alcohol and it will be difficult for them to achieve the targets they set while under the influence of alcohol and we often see them Those who bet under the influence of alcohol will experience failure in the bets they play, of course this is very detrimental, you are right we can drink alcohol but not while gambling.