Any useful idea about the future should appear to be ridiculous.

Strongly disagree with this quote. Some useful ideas about the future might seem ridiculous. But a lot won't. Lots of new technologies and improvements are due to steady fairly predictable improvement of existing technologies. It might be true that a lot of useful ideas or the most useful ideas have a high chance of appearing to be ridiculous. But even that means we're poorly calibrated about what is and is not reasonably doable. There's also a secondary issue that the many if not most of the ideas which seem ridiculous turn out to be about as ridiculous as they seemed if not more so (e.g. nuclear powered aircraft which might be doable but will remain ridiculous for the foreseeable future) and even plausible seeming technologies often turn out not to work (such as the flying car). Paleo Future is a really neat website which catalogs predictions about the future especially in the form of technologies that never quite made it or failed miserably or the like. The number of ideas which failed is striking.