They're VERY good people, and there are some mistakes very good people are less likely to make than others. Peter Parker isn't likely to just forget that his getting drunk is a bad idea-for several reasons-just because he's depressed about seeing Mary Jane, and the idea of a one night stand with someone he doesn't like isn't something that he's on the fence about and just needs a few drinks to overcome his inhibitions, it's something that should be so foreign to the way he thinks that it shouldn't seem like a good idea, no matter how much he drinks.
Justifying anything he's made to do by saying "well, he's not perfect and he makes mistakes" is saying that deep down, he's no better than anyone at all and he's capable of doing anything, no matter how much of a moral failure it is.