President Obama sought Thursday to recalibrate the United States’ response to the Arab Spring, giving new weight to issues of democracy, freedom and human rights in its approach to a rapidly changing Middle East. But although Obama’s words were largely unassailable, they failed to address some of the more difficult realities of foreign policy.

Who could deny the president’s assertion that the United States opposes tyranny? Or that the United States believes in free speech and self-determination and the right of people everywhere to protest peacefully, whether in Bahrain, Yemen, Syria or Egypt? As long as they don’t turn to violence, the president said, the United States will support them in their calls for freedom of religion, women’s rights, economic justice and democracy.

These are long-standing American principles, at least on paper, and the times when the United States has followed through on them around the world have been among its proudest moments. But let’s be clear: To say that the U.S. supports freedom and democracy is easy. In practice, foreign policy is a complicated business, and sometimes a morally opaque one. That’s why the U.S. has so often found itself colluding with repressive regimes or failing to go to war to protect the innocent or turning a blind eye to gross violations of human rights.

Obama didn’t talk enough about the tricky situations. At what point, for example, does it become necessary to go to war to fight on behalf of core American values? Obviously, the U.S. cannot use its military might to solve all the problems of the world, so how should it pick and choose? Nor did the president discuss what to do when our short-term interests clash with our long-term values — as has been the case for years with Saudi Arabia, a repressive, sexist, undemocratic Islamic monarchy that’s been one of the United States’ chief allies in the region for decades (mainly because it sits on vast quantities of the oil that the U.S. economy needs).

And how should the United States choose sides when legitimate interests appear to clash, as in the conflict between Israel and the Palestinians? Obama spoke articulately about the need to reach a two-state solution, but said nothing about, for instance, how to redress the grievances of Palestinian refugees without undermining the very existence of Israel, to which he said the United States has an “unshakeable” commitment.

The president deserves praise for stating clearly that U.S. interests are advanced by a more democratic and prosperous Middle East (and not just by dictators who allow us to drill for oil or base troops in their countries). His determination to put the U.S. squarely on the side of the repressed rather than their repressors is commendable. But he might find it difficult to put his principles into practice, and might find himself explaining his choices again in the years ahead.