We should believe that a glorious future for humanity is possible, and that losing it is a special kind of tragedy.
When every attempt to describe that glorious future sounds unappealing, it’s tempting to write off the whole exercise and turn one’s attention to nearer-term and/or less ambitious goals.
We may not be able to describe it satisfyingly now, or to agree on it now, and we may have to get there one step at a time - but it is a real possibility, and we should care a lot about things that threaten to cut off that possibility.
Personally, I don’t consider myself able to imagine a utopia very effectively. But I do feel convinced at a gut level that with time and incremental steps, we can build one. I think this particular “faith in the unseen” is ultimately rational and correct.