"Hate" is a bad word for what we feel, right now.
First, you should change the word "hate", because it doesn´t convey our feelings correctly. Hatred is blind, our resentment towards Bush is not. We do not "hate" Bush, per se. We hate what he represents, we hate what he has done to the world, we hate the way he thinks, the way he acts, the way he is.

Second.
We are forgeting about the election fraud, the New American Century crap, the Texas death penalty, and the fact that people have a problem not only with Bush himself, but with his entire administration.
Also, i think it´s dificult to distinguish between how much is his policies and how much is his own personnality. He takes the decisions that he does exactly because of who he is, and you cannot resent his policies without feeling some resentment for the man behind them aswell.
People not only "hate" him, so to speak, they are also scared shitless of him, because of what he represents and what he might do (and is doing) to the world.
The man is a political antichrist, opposed to all that is good and decent. If on top of that, you add the fact that he is a complete moron, with an IQ of a 5 year old, you can´t help but wondering what is there to like, in the first place.
If you ask me personnally, i will "hate" the man and i hate his policies, for as long as he keeps the president´s office. The moment he is gone, i won´t have a problem with him anymore. But untill that day, he will always be on my sights.
If he was the president of just the local country club, as opposed to being president of the US, most of the world wouldn´t have any opinion about him. Except maybe a small measure of pitty for all the other club members. It´s his job that spurs so much resentment towards him.
We shouldn´t also forget the Bush family history. Bush the father´s policies are as bit insane as his son´s. The family was made rich thanks to dealings with the nazi party, the bin Laden family, and lots of oil speculation and government favours. The whole family stinks of illegalities, imoralities and indecencies. Seeing both of them reaching office due to dirty money is sickning.
Why do we "hate" Bush so much?
It´s simple: Bush represents all that is wrong with America and the world today. And because much of what happens in America transpires to the rest of the world at large, it affects every single human being.

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"Quincitilius Varus, give me back my legions!"
Emperor Augustus of Rome.