This could be a very interesting discussion, but before getting into it in any detail, I think your perspective needs some refinement. Esteem for modern art, including modern architecture, strongly correlates with the sorts of utopian thinking that you list as an essential feature of the "pro-nice" side. Imagine you read someone you've never heard of harshly denouncing modern art and architecture as ugly, pointless, and dehumanized garbage -- what other attitudes would you guess this person probably has?
(As for brutalism in particular, it took these buildings to actually be built, and people to be exposed to them for a while, for their sheer horror to be truly felt. Once this became evident, the style was soon abandoned. But it is clear that back in the day, the people enthusiastic for that sort of thing would have been disproportionately, if not overwhelmingly in the "pro-nice" camp, just like those enthusiastic for the presently popular forms of modernism today.)
This leads to one of the major contradictions in the way you try to draw the lines. Seeking "naive prettiness and pleasantness" can have the form of desire to find for oneself a small pleasant corner of the world to live in, without any inclination for idealism -- either theoretical or practical -- for the rest of humanity. Often this attitude is accompanied by a strong (and typically justified) hostility towards idealism as dangerous nonsense that threatens to upset the peace. Here your model seems to break down.
As for brutalism in particular, it took these buildings to actually be built, and people to be exposed to them for a while, for their sheer horror to be truly felt. Once this became evident, the style was soon abandoned
I think I must be the last person left on earth who actually likes brutalist architecture. The term seems to have become something of a whipping boy, but I think most people who use it derisively have never actually seen any good examples, and are just thinking of the big rectangular government buildings.
Maybe I'm just prejudiced because...
EDIT: This post is pretty flawed, but please read the comments anyway: I'm hoping to rework it into something that catches the idea better.
You can view a lot of value differences along a pro-nice/anti-nice spectrum.
Pro-nice people (I'm one) gravitate to obviously pleasant, lovely, happy experiences. We like kittens and puppies and rainbows. We like transparently "happy" music and transparently "beautiful" works of art and literature. (If you like Romantic poetry and science fiction, but not contemporary novels, you might be pro-nice.) We prefer the positive social emotions, like sympathy, encouragement, and teamwork. We may choose intellectual interests based on the fact that they make our brains feel good. We tend to be drawn towards proposals for making the world wonderful.
Pro-nice people aren't quite the same thing as optimists. An optimist tends to anticipate that things will turn out well, or look on the bright side. But pro-nice people may well hold pessimistic ideas or have melancholy temperaments. Pro-nice is a preference for the positive. A typical pro-nice attitude is "Humanity may be destructive and cruel, but the one time when we're at our best is when we're doing science. Science is lovely. I think I'll be a scientist."
Anti-nice people have a preference for the difficult. They find pro-nice preferences saccharine. They like artistic expressions that have a challenging or negative "mood." They prefer the negative social emotions, like antagonism, sarcasm, and cynicism. They dislike things that have obvious appeal, or things that everyone finds pleasant. As far as social issues go, they take a keen interest in potential catastrophes and what must be done to avert them; they generally aren't drawn to proposals to "make the world a better place."
Again, anti-nice people aren't necessarily pessimists or unhappy people. Anti-nice people prefer to direct their attention to the challenging, the problematic, the worst-case scenario. To an anti-nice person, there's nothing interesting to work on when everything is going smoothly; just liking things or agreeing with people or being contented is rather dull.
I suspect that a lot of conflict can be summarized by the clash between pro-nice and anti-nice personality types.
Are you pro-nice or anti-nice? Have you experienced difficulty communicating with the other type?