Um. Alright. I wasn't really commenting on Tito's plan, but rather on MichaelSmith's notion of a one-way trip, at the start of this thread (which, btw, has been proposed, seriously). But sure, let's get serious if you want.
I do see a point in sending meatbags to Mars. Not for the sake of a flyby, or that joke about the flag, but ultimately to attempt to live in Mars for extended periods of time. Staying in Mars, in some sort of habitat, establish a permanent presence in another planet. I think achieving this should be considered a more pressing issue than it actually seems to be. I'll come back to this in a minute. But a flyby may be useful, to assess what exactly it takes to get there.
First though, I'm not sure you've got your numbers right. Valeri Polyakov stayed 14 months aboard that tin can, Mir. Sergei Krikalev (who's spent 800+ days in space) stayed 10 months while the USSR dissolved. Aleksandr Kaleri has spent almost as long - he was in the ISS couple years ago (and the man is 56 btw). And so on. Now of course there have been side effects, both physiological and psychological, but, to my knowledge none incapacitating, and none permanente in the long-term. So I'm not quite sure, when you say "Humans cannot sit in a tin can for two years and retain sanity", what are you basing this opinion on? I'm not an expert, but given these numbers, well. To me, it sounds very hard alright, but not impossible, or even unrealistic.
You also said, "We already had ground simulations of the flight, and they were generally unsatisfactory". Could you elaborate? I only know of Mars-500, an experiment conducted by a few years ago where they isolated a crew to simulate a trip to Mars. I recall they all completed the experiment, no one went bonkers aboard and started killing the others, really. I seem to recall there were issues concerning lack of sleep, which of course is serious and needs addressing. It may be part of the reason why ISS astronauts take sleeping pills now. In any case, experiments like Mars-500, valuable as they are, can't simulate microgravity or what I think will be the worst issue, radiation. So I do see a point in those lab rats in a tin can, harsh as the whole notion is.
I hear you on that part about research, that's always a necessity. But I don't think there's a reason why it must be one or the other, we could have a manned mission *and* research into new technologies. Thing is, and again I may be misinformed, but I don't think we're even close to develop technology that could cut the flight time substantially. I mean, we don't even have the science, the theoretical groundwork, on which to base such a technology. Travel to Mars in a day or two, you say? Come on, man, get real. That's going to take a very, very long time to achieve, and I don't think we should wait that long.
The reason why I see this is a pressing matter is: I think it's paramount for us, as a species, to hedge our bets, as it were. To make living in another planet, if not economical or practical, at least feasible. Because we don't know when the next Chixculub rock is going to hit, we don't know when we'll face a pandemic that wipes life on Earth, it can happen any time. And I think it would be immensely valuable to know that such a scenario wouldn't necessarily mean the extinction of the species.