The problem with that argument, langeweile, is that there are LOTS more people being oppressed FAR WORSE in other countries, and the US *IS* sitting by and doing nothing.
It has little to do with "liberating" the Iraqi people. Don't fool yourself. If that was the reason, why the need to go in for WMD?
The alternative to the US not being "policeman of the world" is doing what we HAD been doing, somewhat successfully (not entirely, mind you) for fifty years - using the UN. And if you claim that the UN is broken and the world has stood by and watched while bad things have happened, you'd better start by looking at the US' history of voting on resolutions about these places first. Rwanda leaps to mind. The US is NOT proposing to "help the weak and oppressed". They are proposing to intervene where and when they want, for whatever reasons they want. Anybody interested in helping the less fortunate of the world is going to have to look elsewhere - like, to the UN, where they often have.
The UN was, and could be again if the US would come back to the table and pay its dues, a very useful organization. It did what it was essentially designed to do - prevent another World War. To its credit, it was just *starting* to involve itself slightly more proactively (read, forcefully) on genocidal and related humanitarian issues. It is a work in progress. The US has abandoned that work to establish itself in a very precarious position, one which endangers much of the work that has been done since the end of WWII.