Agreed.
Disagree. There are many settings and games, including modern ones, that utilize black-and-white morality effectively. I mean, can Thanos have a good "logical" reason for wanting to rid the universe of half its populace? Sure. But that doesn't make him gray. I think people confuse this at times. Heck, Lord of the Rings, Evil Dead - Army of Darkness, Big Trouble in Little China, Dragonlance, Elfquest, etc. all made a good story using black-and-white morality. Simply because the protagonist and antagonist have "reasons" for their actions that don't specifically align to good-evil, doesn't mean the hero-villain contrast isn't clear and the known supported outcomes aren't clear to each.
There is a big, big difference between "there are heroes and villains" (which I am in favor of!) and "
full-on black and white morality". (Emphasis added.)
The former can have heroes who kinda suck as people, but still
ultimately choose the right thing. It can have villains who are genuinely redeemable, whether or not they actually do achieve redemption. (Redemption is not easily achieved and many who seek it will not find it; this is a sad truth, but a truth nonetheless.) It can have heroes who genuinely
fall, not from being tricked, not from misunderstanding a half-heard conversation, not from a single impulsive act, but a knowing and eyes-open march into the arms of evil.
The latter has no room for any of those things. Everyone who is a hero is 100% pure hero. They cannot have undesirable characteristics (whatever the person writing thinks is undesirable). They cannot do bad things, ever, even for good reasons. At worst, their greatest "fault" will be either being kind of preachy/anvilicious, which will be spun as "if the evil people weren't evil they wouldn't need to do this",
or being slightly impulsive, which will be spun as being just so gosh darned
eager to do the right thing. Meanwhile, the villains will be pure awfulness, beneath contempt for how morally, and more importantly
socially, repugnant they are. (Again, depending on what the author sees as morally and socially unacceptable, which will usually be conflated.) Redemption will never occur because anyone who has ever done wrong cannot be Good, only the
pure can be Good.
Hence:
full-on black-and-white morality is essentially always boring, because it reduces characters to their jersey and whether or not it has even the slightest stain on it. It's also usually
very propagandist, because it selects some specific trait(s), affiliation(s), belief(s), or behavior(s) which are Acceptable Targets, things to be vilified, scorned, and (ideally) destroyed. That's where queer-coded villains come from, or where the token fundie comes from: ink-shadowed acceptable targets for the pure-as-the-driven-snow heroes to destroy with extreme prejudice because they
deserve it, for being so
horrible.
Consider this concluding paragraph from the TVTropes page on Black-And-White Morality:
"Please note even in a world where the moral lines are sharply drawn, there may still be characters or organizations that are presented as being 'grey'. A general rule of thumb as to whether or not black-and-white morality is present is that the heroes are almost always considered to be in the right, while the villains are always 'wrong'. Of course, the audience might disagree with the author's moral compass."
A world having sharp moral lines is not the same as that world being "full-on black-and-white morality". Sharp moral lines just mean that there's a very clear division and that, at least on some axis or axes, there's no fuzzy boundary. That's pretty normal, even IRL; crimes meriting capital punishment (where law does not forbid capital punishment), for instance, tend to be
very much sharp moral and ethical distinctions and there's at least some degree of "if you did this, there is no forgiveness". "Full-on black-and-white morality" means there are
never shades of grey about anything at all. That the heroes never do anything wrong except, perhaps,
very briefly as a mistake, generally because they were misled by another. Heroes functionally never do wrong, and villains definitely never do right.