I agree with you that 'terrorism' is better defined as a tactic specifically used by criminals (but also, I'd say, by states and other powerful institutions), but I have no reason to suspect that the war on terror is a war on ideology. In fact, I think that framing this war as an ideological one masks it within a context better understood by maybe a majority of fundamentalist Americans and probably many media-informed Americans. I think maybe it allows the war to appear more justifiable than it really is.
The war, for all intents and purposes, seems really to be a war simply for oil, and that may explain your confusion over why it is that America considers itself violently opposed to the ideologies of the Islamic world. It isn't, honestly, and I believe our goals for this war are really that ignoble. It's unfortunate, from my point of view, that some would allow lives to be lost to provide economic stability for this nation, I would much rather give up energy and work together with others to find a better, more utilitarian way of living comfortably in the west. It's very frustrating that innocent lives are being thrown away on both sides for an empty war, a war sustained by capital and oil tycoons.