Any modern reader, after parsing the language, will react to the Alien and Sedition Acts with a "How can this be legal? Seriously?"

Short answer? Because the president and Congress said so. This was before the concept of judicial review, so ironically enough, that tyranny the founders railed against could be managed so long as the legislative and executive branches were held by the same party.

While the Naturalization Act isn't really on shaky ground, both Alien Acts are, and the Sedition Act might as well have been just a picture of a man burning the First Amendment. It's important to note that the hundreds of years of tradition and reverence for the Constitution (or at least what we believe the Constitution to be) hadn't happened yet.

The idea of amending or changing the Bill of Rights wasn't completely off the table. In fact, the Constitution was intended as a living document, something proven by the Bill of Rights itself. "Amend" means "change." The founders went ahead and changed it ten times before the ink was dry.

Jefferson and Madison, however, recognized that the Alien and Sedition Acts were an assault on what they believed was one of the bedrock principles of the United States. Unlike now, they couldn't just say "because the First Amendment" and expect to win arguments. They had to resort to arguments, and in Jefferson's case, the ill-advised creation of a new concept that would mess everything up in another sixty years.