As a recovering alcoholic with 17 years of hard drinking behind me, I can state that I've witnessed and experienced an unlimited number of reactions to alcohol in the circles I used to frequent. In many cases, I agree; alcohol does tear down one's personal inhibitions and people say and do things that have been lurking inside and which they would otherwise supress. Having said that, I've observed that a hardcore drinker, especially one who has abstained for a protracted period will experience a Jekyll and Hyde effect, doing things that are completely out of character for them.
I'm not making excuses for Gibson, and have been critical of him elsewhere in this forum, as I would be with any recovering alcoholic who surrendered their sobriety. Having said that, Gibson also has my pity and prayers that his apology was sincere, and that he will learn to value his sobriety above money, ambition and achievement.
When things are going bad in our lives, it is human nature to pray to God that he give us no more than we can handle. Far too infrequently, do we fail to pray that God limit our successes to that which we can handle as well, and I would suspect Gibson lost sight of that.
Is Gibson an anti-semite? I haven't the vanity to pretend to know what's in another man's heart. Did he open his heart for the world to see when he got loaded? It's possible, but far from certain.