I think the original poster's title for the thread has just been misleading people and diverting attention away from his point. He wasn't saying Bitcoin mining was "pointless" in that it shouldn't be done or has no value (assuming of course that Bitcoin ought to be participated in and has value itself). He was saying that it's not a logically necessary requirement that the mining activity not have positive spillover effects.
I think you are right. The thread title is a bit misleading and perhaps it should be changed. So in a sense the OP wants the proof of work mechanism to perform some function that not only is of value to the bitcoin network but also have some external positive social benefit. I think the idea is noble in and of itself but what on deep inspection it may be a bit impractical and difficult to implement technically.
I keep wanting to return to gold as my example. Say you go back in time and, somewhat impolitely, pretend to be an Aztec god and have the opportunity to convince the Aztec people to use either gold or some alternative to gold. Gold and the alternative have, for monetary purposes, similar properties: they're equally rare, equally distributed throughout the earth, take roughly equal resources to mine, and so on. If you were trying to help the Aztecs, wouldn't you want to look at whether the mining process for gold, versus its alternative, happened to lead to positive or negative effects unrelated to the use of the object of the mining as a currency? For example, maybe in the process of mining gold, the Aztecs will discover valuable sources of water or other information about what lies below the earth, whereas mining for the other, they won't. Maybe mining for the other will ultimately poison them, whereas mining for gold won't. Why wouldn't you look at those considerations when choosing the properties of the future currency?
In designing Bitcoin, which is of course an ongoing process even now, the community has that choice. It's not a question of whether mining is "pointless"; it's a question of what to count as "mining" to make it have value beyond, perhaps, its value to the Bitcoin network alone.
The question is who decides what should count as "useful" mining? How do we go about changing the nature of the mining work (hence the nature of the proof of work mechanism) on the fly when it is decided (by whatever mechanism) that the current mining work is no longer useful or is not bearing fruit. Will changing the mechanism cause incompatibility issues in the network. Will altering the mining work somehow "centralize" the decentralized nature of the bitcoin currency (reason being something has to tell each miner what new type of work is required of it - that something would most likely be a single server or cluster or some single entity)?
Also what if changing the mature of the mining work creates an added value? Whom stands to benefit the most from this added value service? Humanity as a whole or a specific group of individuals or corporation or vested interests? Let's take for pharmacological computational work? Who will benefit from any potential discoveries that come as a result of this mining work? Who own the rights (and therefore profits) to any beneficial discoveries that come about as a result of the mining process?
These are all questions that need to addressed. Sure it sounds noble and it would be *nice* if the mining process resulted in something of benefit to everyone. Lol I think at that point bitcoin would become backed by altruism in as sense - I'm joking of course.
Also am I mistaken but shouldn't the ideal currency have absolutely no tangible benefits whatsoever? After all we don't use water as money do we? Gold is not the ideal currency but it very much closely approximates that ideal. Bitcoin in a sense is the perfected ideal currency. I think that bitcoins should have no "benefit" and no inherent tangible value other than that which its USERS give it.
Granted I'm no economist so I may not know what the hell I'm talking about