I think you're being too harsh. Right now silicon use is of course wrapped up in a loop of value derived from the coins being mined having value, but that completely disregards the actual value of the blockchains. An excellent quote I found is: "how to recycle what will soon or later be a HUGE obsolete distributed supercomputer dedicated to SHA-256."

>that completely disregards the actual value of the blockchains

It doesn't. I just think the value of blockchains is near zero. I have yet to hear of any problem that isn't better solved with a normal database.

There is one problem that the blockchain solves.

It can make a large hostile network with extremely high computation resources act like a single computer with the performance of a 10 year old desktop.

What about something like folding@home?

No floating point whatsoever. That's the "application-specific" part of "application-specific integrated circuit."