Again, the First Amendment has its limits. If some organization were to publish a "you can build it at home in your spare time" cookbook recipe of how to create an innovative sort of nuclear weapon capable of destroying a large city, I'd expect for the government to step in and prevent its publication and sale... purely as a matter of national security. Now THERE, it's true that getting "enough" nuclear fuel is nontrivial, but in the case of biological (and even some chemical) weapons, the potential for actual (and not just imagined) mischief is far greater, and the harm that could be done is far too high to dismiss as being simply hypothetical until after the fact.
Are you aware that fairly explicit instructions were just last week published on the internet for building basement nukes? Sorry, you are dead wrong -- the First Amendment has no limits. And anyone who thinks so plainly needs killing.