leaving aside Iraq for a moment, what is the central principle of our foreign policy under the Bush Administration? That can be surmised by looking at who, exactly, is directing foreign policy. Nominally, Sec. of State Powell would have that role, but in reality, there are a core group of people advising President Bush, the Neo-Conservatives.
The label "Neo-Conservative" (neocon for short) is often broadly applied to anyone disagreeing with a liberal agenda, even with regard to domestic politics. It is somewhat more accurately but still too-broadly applied to those who favor an attack of Iraq (for whatever reason, on either side of the politico-ideological divide). The real neocons are a core group of defense and foreign policy advisors during the Reagan Administration, including Richard Perle, Paul Wolfowitz (current Deputy Secretary of Defense, was Under Secretary of Defense for Bush 41), Donald Rumsfeld (Secretary of Defense, for both Ford and Bush 42, as well as multiple advisory posts under Reagan). Other prominent neocons include William Kristol (who funds the Weekly Standard), Norman Podhoretz, George F. Will, and William Bennett. Modern neocons include Stanley Kurtz and Michael Ledeen (both writing for National Review).
FACT. The central tenet of the Neo-Conservatives is that all foreign policy, especially that pertaining to the Middle East and Persian Gulf, should be aimed at benefiting Israel.
This is the bedrock belief of the neocon agenda. All foreign policy is derived from this cenrtal principle, and recent events simply are shoehorned into that principle.
Yet, the rationale is sound from a certain pragmatic perspective - Israel is the most successful of our client states, dating back to the Cold War (whose domination-via-proxy mentality still dominates the thinking and viewpoint of most of the neocons mentioned above). Our financial support for Israel is the primary engine driving Israel's growth as both an economic and military power (myths about making the desert bloom notwithstanding). As Steven Den Beste has noted, Israel is our client, not our ally.
Curiously, neocons share the goal of Neo-Wilsonians in promoting democracy (at least nominally). But this is misleading, as these two competing schools of thought are actually diametrically opposed. The central difference between neocons' and neowilsonians' approach to proxy client states is the answer to this question:
"After American-directed regime change of a nation, and installation of democratic machinery for self-government, should the people of that nation be allowed to elect an anti-American leader?"
This question applies to Palestine, to Iran, to Afghanistan, and of course Iraq. The neocons will say "No." and the neowilsons will say "Yes".
The consequences of saying "No." are clear - that is why we have corrupt and dictatorial regimes in Egypt, Syria, and most notably Saudi Arabia. In a brazen display of hypocrisy, the non-democratic nature of Arab regimes are used as an argument for neocons' wish to extend American military intervention beyond Iraq to the entire region. Presumably, they would effect regime change in all these nations, and then again deny the people there the right to elect leaders unfetterred by American strategic concerns. This will again lead to dictators and oppression, as well as cauldrons for terrorism, and become targets for the neo-neo-cons of the future.
Israel's security is something I strongly favor. The neocons' prescription for Israel's security is to endlessly destroy nations surrounding Israel until eventually they give rise to pro-American democracies. This will only result in Israel's insecurity.
The neocons are the worst enemy that Israel has ever had.
I assume that an invasion of Iraq is a given, regardless of Congressional deliberation or UN resolutions. Once the war has begun, it will be conducted entirely on Bush's terms. That is how the administration has pursued domestic policy and that IS how it will pursue foreign policy.
So, after invasion, then what? There are still good arguments to be made for invading Iraq. But these (quintessentially Neo-Wilsonian approaches) require a kind of commitment to nation-building that the Bush Administration is incapable of making
I also highly recommend this series by Zachary Latif, on the Right Way to effect regime change in the Middle East and the Persian Gulf. This is the kind of analysis that the Bush team should have been making a public case for. In some sense, neo-wilsonianism is anti-imperialist imperialism. It takes an imperial power to set right what an imperial power previously set wrong.
The consequences of invasion according to a neocon game plan, on the other hand, are going to be bloody. There are legitimate comparisons to Vietnam. Worse, in fact - there are legitimate comparisons to the Israeili-Palestinian violence. Iraqis are not likely to simply lay down and embrace American troops as saviors the way Iranians would, since the general sentiment in Iraq is pretty hostile
Note that some conservatives, addicted to the neocon gameplan, have already called for re-instating the draft. (For a thorough discussion of why Selective Service should be abolished, and why the suggestion of a draft is so anti-American, see this Libertarian page quoting Ronald Reagan and John McCain. Also, Steven Den Beste has a nice essay on the value of a conscripted military.
Certainly, Afghanistan was a short-term success, though even with Bin Laden most likely dead, it may have increased the threat from terrorist groups like Al-Qaeda rather than decreasing it, by dispersing them far and wide. And Afghanistan is far from stable. It was our failure to properly rebuild Afghanistan after using it as our proxy against the USSR during the Cold War that caused such strife there, that the Taliban were (initially) welcomed into power. The Taliban's rule created the Al-Qaeda safe haven, leading to the attacks on 9-11. What lessons does this cycle of cause and effect hold for Afghanistan II, as well as for Iraq? It's impossible to say. But success in creating a stable and democratic proxy requires a Wilsonian approach, not a neocon one.
The neocons may be thew worst enemy democracy has ever had.
There is a difference between neocons and warbloggers. Warbloggers are those favoring military attack on Iraq, but aren't necessarily neocons. Many warbloggers, for example, are liberals or moderates who simply believe that invasion of Iraq is necessary based on their reasoning from teh facts. These include Steven Den Beste and Glenn Reynolds.
 for domestic political reasons. Must.. Have.. Tax.. Cut... and Israel and Iraq can't BOTH be our Bestest Favorite Proxy Client Nation, because that would mean splitting the pie$$$. Strategic and political foreign aid is a zero-sum game).
 I have confirmed this from many people I know who live in or have visited Iraq. Iraq is home to several important religious locations to Shi'a muslims, and so there are always many pilgrims traveling there.