I am extremely pro-manned space travel, but in order to be successful, it has to be done right. There has to be a reason to go - so that we know what to do when we get there. As Rand Simberg noted, we need a vision, not a destination - and Bush has failed to deliver.
First: in the wake of Columbia, it's reasonable to demand an answer to the question: Why should NASA be trusted with a Mars shot? Can NASA achieve the balance between safety and quality? Keep in mind that the last time NASA came up with a manned mission plan, in response to President George Bush's call for Mars exploration in 1989, it was a $450 billion monster that dubbed "The Death Star" (That's ~5 Iraq invasions and reconstructions for those of you keeping score).
What we really need to do, in the wake of the Columbia disaster, is re-think the very purpose of our manned space infrastructure. This means asking common sense questions about our needs. For example, what purpose does the Space Shuttle serve? Is it to ferry astronauts to the Space Station and back? We are currently doing the same job using Soyuz technology, upon which the Chinese Shenzhou 5 is based (with modernization improvements). Shenzou performed flawlessly, and NASA has indicated that they are leaning towards a capsule derivative of Apollo as well.
Do we need the Shuttle to lift cargo into orbit? The same task is achieved by Atlas and Delta rockets. Even the aging Titan is still being used on occassion. We don't need manned flight for simple heavy lifting.
We also need to ask the basic question of why are we going to Mars? For symbolism? We don't have a Cold War to fight against a symbolic enemy anymore, against whom the US flag planted on the soil of Mars could be used as a propaganda victory.
If we are going to Mars for science, then we need a lot more unmanned missions first (keep in mind that of all the missions launched by Russia, the US, and Europe, only three missions have succeeded in safely landing a functional probe). The reason is that given the enormous expense and risk of sending a human to Mars, we cannot waste the precious human work-hours on teh surface when we succeed. The basic science needs to be done ahead of time so that our astronauts are not doing manual labor and drudgery, they can focus on the true science. We need to establish a baseline of data so we know what our manned mission's goals will be.
And the mechanics of HOW we get to Mars need to be thought out very carefully. We need to make a commitment to research that facilitates the goal, and I don't see that commitment in NASA's funding. Why did funding get cut for the TransHAB crew module? It would have been an ideal crew compartment for the long transit: an inflatable three-story cylinder where the drinking water doubles as a radiation shield. It could have been tested on the Space Station first. But it's gone.
Also, where's the funding for basic research on extracting water from the soil? oxygen from the crust? There's so much basic science research that needs to be done if any Mars colony is going to be self-sustaining for even a short period of time.
It's not clear that Bush has even considered any of these issues. In fact, it's far more likely that it's another political ploy to portray himself as the Vision president. But looking at the Administration's own record of statements about Mars, it's not hard to discerns the true motives of this policy proposal. The most incriminating piece of evidence from the UPI story though is this little buried blurb:
Sources said Bush will direct NASA to scale back or scrap all existing programs that do not support the new effort.
This betrays a profound ignorance on what NASA's purpose is for, and makes it hard to believe that there's any serious policy intent here at all.