Why not? With Obama in charge, we aren't going to do good anyway and the Europeans need to shoulder the costs of their own military defense, such as it is. Withdrawing is against the concept of the US as a superpower who guarantees world stability, but those days have passed with Dear Leader in charge. If anything, he is busy destabilizing countries and spreading the Muslim Brotherhood and other Islamists with US power.
Just because Pandora says she can handle the cost of keeping the box does not mean you leave her alone with it to open it.