The US tried isolationism in the 20th century. The result was two world wars that we couldn't avoid becoming involved in. The fact is the US is the 800-lb gorilla on the world stage, and it cannot isolate itself from what happens in the rest of the world, however much it might try. And after the experiences of the last century, we no longer try. In a world where terrorists and rogue states have the capacity and the desire to visit destruction on us right here in this country, there are few voices today crying out for a head-in-the-sand approach to foreign policy.
BTW, I very much disagree with those who claim the US intervenes in other countries in order to profit financially. As huge as the US economy is, the contribution of the resources of any country the US might be tempted to intervene in would literally hardly be noticed. We are even close to being net exporters of petroleum, which many claim as the motive behind US activities in the Middle East.
Much more than money, what the US seeks through its foreign policy is stability rather than political upheaval. That has sometimes put us in the position of supporting repressive regimes when it seemed the alternative would foment greater instability or uncertainty. On the other hand, as our current policy toward Syria shows, when it's clear that the policies of the regime in power will in themselves cause political instability, the US may support dissident political movements or even armed rebels.
Bottom line: at this point in history US isolationism is simply not an option.