The Washington Times did a piece on micronations, including the “Empire of Atlantium.” The article cites a few examples of individuals attempting to live outside the control of the state, but it doesn’t address the issue at hand: is secession of individuals legitimate?
John Locke was rather confused on this issue: he said that the consent of the governed was essential, but that getting explicit consent was impractical (see chapters 8 and 9 of his Second Treatise). Lysander Spooner was more radical in his No Treason, arguing that those who did not explicitly consent to be ruled by the Constitution cannot be bound by it.
The secessionists discussed in the Times have been largely ignored by the governments from which they seceded. But it seems obvious that were these “micronations” a threat to the statist quo, they would be crushed.