"known-bad" ... defined by you? Cause if the best & brightest did it (in this case SETI@Home) it seems they disagree with that categorization.

Well, one used maybe tens or hundreds of megawatt hours over the course of a year, while the other uses tens or hundreds of terawatt hours per year.

One was a launching platform for dozens of scientific and other large scale volunteer computing projects, and the other's value is entirely based in speculation.