Amendment I takes precedence over Article I. Congress does not itself get to decide what "the people" refers to in the Constitution, and acts of Congress do not alter or establish any meaning of any terminology in the Constitution. Where there is ambiguity, the courts resolve it -- Congress does not have the final say in interpreting the rules that define and limit its own power.

Further, the protection of free speech in the first amendment does not even refer to "the people", but simply prohibits Congress from abridging the freedom of speech per se, without qualification or any exception for who is doing the speaking. Congress cannot pass laws that abridge the freedom of speech as a matter of actual effect, regardless of whether they are doing so under the auspices of exercising other powers.

Foreign policy powers don't come into it -- if the act restricts free speech, it is unconstitutional, regardless of what end Congress was attempting to pursue.