As I said to another poster, morality gets into subjects that are forbidden here (politics and religion) and I'm going to quit discussion the topic.
My point was that during prohibition, 1 day drinking alcohol was legal and the next day is was not. Either people that continued to drink were moral or immoral and that didn't really change when the law changed, IMO.
First, unfortunately, you're trying to argue an exception rather the rule. You can always find exceptions, but those exceptions don't negate the general rule, which is what my point is about. In general, laws reflect a society's morality. It doesn't matter whether those laws change at some point in the future. If it is illegal at the time in which you live, then, according to society, it is the wrong thing to do.
Second, you have to look behind the law to determine what the law is trying to address and whether it can be adequately addressed broadly or more specifically.
For example, what was the purpose for Prohibition? At that time, our society feared the consequences of drinking alcohol because it could lead to drunkenness that could harm others. Harming others is wrong. But because the cost of maintaining Prohibition was so high for society and because our society values personal freedom more highly, people at that time felt it wasn't worth it to maintain Prohibition.
But the reason for wanting Prohibition is still valid, which is why we have laws against driving while drunk and public intoxication. Notice, we may have done away with Prohibition, but we didn't do away with laws dealing with the negative impact alcohol can have on a society.
Instead of broadly dealing with the issue of alcohol, we deal with it on a more specific level. But we still deal with it via the law because our society want people to know that driving drunk and inappropriate public displays of drunkenness are wrong.
