Why? The US involvement in WWI led to the harshness of the Treaty of Versailles, if the US held back it's been argued that England and France would have sued for peace earlier and the harshness of the treaty wouldn't have been there and then one of the prime causes of WW2 would not have existed.
The Us involvement in WW2 is due to escapades in China and the Philippines - the reason Japan attacked the US.
The fact (well, I agree) that the US badly screwed up its first really major intervention in world affairs has little to do with the present day, unless you contend that we learned nothing from it (e.g. for WWII Unconditional Surrender and the occupation and nation building we did in Japan and West Germany).
I'm arguing that non-intervention might be good; that perhaps interfering with other countries might not be a good idea. Now I'm all for humanitarian assistance, and helping people fleeing countries that are war torn. In fact, I think when their is serious strife the US should do it's best help people relocate to the US -- e.g. instead of letting people get slaughtered in Rwanda we should have helped evacuate them to the US.
I think that it is far from given that the US should be the world police, or that anyone should be the world police.
The Us involvement in WW2 is due to escapades in China and the Philippines - the reason Japan attacked the US.