Notice I said mild alcoholism, not mild drinking. On the scale of alcoholics (who generally can't get through a day without drinking) I think this is probably mild. But it's just semantics.
Heavy alcohol use among teens, even those who aren't dependent on it, has been shown to damage prospective memory well after the alcohol has cleared from their system. The damage lasts for months, at the very least.
I think it's entirely appropriate to consider the negative effects of previous decisions even if one is unable to mitigate them. Choosing to ignore them seems like an unhealthy attitude which could contribute to future mistakes.
I often wonder if the mild alcoholism of my youth (drinking to blackout roughly once every month, starting at age 16) has given me any lasting impairment. Certainly, I have no terrible damage since I am highly functional at an intellectually demanding job. But I've always wondered if I took an edge off my memory. My "prospective memory" (remembering to complete tasks without reminder) seems to be much worse than average, but it's hard to tell if this is within natural variation and, even if so, if my alcohol use affected it.
I've read in a few places that alcoholism in children and teens leads to demonstrated long-term memory effects, especially for prospective memory. Does anyone know the level of alcohol consumption at which this effect becomes measurable? Is this damage permanent? (My google-fu seems inadequate.)
I suspect that researchers simply don't have the data to make precise confident statements about damage that is marginal (and, hence, is hard to measure).