You know you've met a visionary when they start talking about solving problems others think are too hard.
It is super easy to throw up all sort of reasons why some grand vision won't happen, here are but a few of the classic excuses:
Now each of these may be kinda true. But I say:
Problems tend to look worst to the people who know the most about them, they can see all the gotchas etc, but have you ever notice how things only seem to happen when you do something? Sometimes things that look hard aren't that bad once you actually try. Knowing a lot is great, but you should never use it as an excuse to not strive for improvement.
Academics are typically not as connected to users as you are, which means you can redefine the problem, into something that is both useful and, this is the key, can actually be solved.
Okay so in 19xx so and so tried to solve the same problem and failed or produced another set of 'intractable' problems, the fact is it is now 2008 and a whole lot of things you couldn't do back then are trivial now. You know the whole standing on the shoulders of giants thing.
The lessons of the past tell you how to fail, but the lesson is not: don't even try.
Sure it is hard/impossible to solve a problem 100%, but that doesn't mean the 80%, 60% or even 1% improvement you get trying isn't worthwhile!
One size doesn't fit all, sure. But life is full of patterns, not all of which have been catalogued. So don't try to stop someone from looking for more patterns, occasionally they might actually notice one that is useful.
I suppose it boils down to this, rules are all well and good, but we should never be tempted to over apply them, the world isn't black and white, ambiguity rules OK.
The real question then is Why not?