Y does X. Y is a basically good person. Therefore, X must be okay.You hear it from all sides of the cultural divide.
"Joe and Fred are married. They're good people. How can you say that that kind of relationship is wrong?"
"Cindy does that. She's a good person. So how can that be racist?"
Think back a bit, and you'll see that a huge number of the casually-made moral arguments one hears these days boil down to this.
There are a couple big problems.
For starters, what exactly is a "good person"? Often this seems to be a category with as little meaning as "someone I like" or "someone who's not obviously engaged in genocide or kitten torture at this moment". And yet, the way the argument is deployed, once someone is determined to be a "basically good person", every action that person takes in now "basically good". It is as if each person is now a good or evil deity, and all the actions of the good deities are necessarily good because good deities can not do evil.
But of course, each person performs many actions. Surely not all the actions of "bad people" are bad and of "good people" are good, if only because "good people" and "bad people" at times do the same things.
A bit of this ties in with the issue of moral fashions. Sins which are currently in fashion, things "basically good people" do, seem like they can't possibly be that bad. At the moment, you're much more likely to know someone who's had an abortion that someone who's killed someone in a duel. Does that mean that dueling is worse than abortion? Well, not necessarily. At another time, one might have been much more likely to know a duelist or a slave owner than someone who'd had abortion. Those sins seemed normal and excusable. "Basically good people" did them. But the sins themselves have not changed as social standards have. Standards of "basically good", of social acceptability, have changed, but moral laws have not. (And for those with an affection for the past: Just because dueling and slave owning were done in distant and more picturesque times does not mean that they weren't just as painful and evil as more modern sins.)
I think underlying much of the urge to identify "basically good people" and excuse their actions from being any serious kind of sin is that by "basically good people" we tend to mean "people like me". By ruling that the actions of "basically good people" can't be all that wrong, we implicitly say that our own actions can't be all that wrong. We restrict sin, you know, bad sin, to being something done by "people not like me". Like Nazis, everyone's favorite example of sin. We all know that's "evil". And if that's evil, and I'm not a Nazi, then surely whatever I do can't be evil, right?
What we need to realize is that people themselves are not good or evil. Actions are. You and I do evil things at times. People like us do evil things. Evil is not something foreign that only people in some other category from us do. It is something that all of us are tempted to and which we all must fight. Unless people realize that evil exists, and that people like them do it, they cannot successfully fight it.