I have so many objections!
I don’t think SF is necessarily about predicting possible futures. I’ve always felt that SF is more like surrealism. The idea is to shock people into awareness. Show them how odd the world is. Whether or not you draw on realistic tropes is irrelevant. But my personal bent is always to try and make the science plausible.
Let it be said that futurism and SF are quite different endeavors. A rude person might say that futurism is about feeding inspirational received truths to businessmen and telling them it will help them make more money. SF is about unruly artistic visions.
Writing responsibly about socially important issues can be timid and boring. The thing is, science really does change a lot over time. Compare what we’re doing now to what we were doing in the year 1000. A Mundane SF writer of year 1000 might want us to write only about alchemy, the black plague, and the papacy.
Rudy has also submitted it as a longish letter of comment to The New York Review of Science Fiction, which has just published Ryman's Manifesto. And it will probably appear there, But at NYRSF, we don't do color illos, and Rucker's blog version of this comes with delighful illustrations that function as a separate stream of visual commentary on the subject.
What I like best about Rucker's anti-manifesto is that it makes me want to sit down and write something fun: cancel the boring meeting with the school district I'm so anxious about; buy the kids ten interesting colors of house paint; and tell them to just paint the house while I sit down to Write Some Fiction!