Is there any principle in law that says that unregulated
inventions/technologies are illegal?
None. Your colleague is totally wrong. Your colleague's position inevitably leads to the conclusion that --since its invention-- the wheel is illegal insofar as it constitutes unregulated technology.
Laws are a dragging and oftentimes distortionary reaction to technology. In theory, regulations are devised to harmonize interests and prevent/mitigate/remedy undesirable ramifications of an innovation. But in reality, regulations oftentimes are the mechanism by which policy makers and judges hinder the adoption of new inventions and natural progress. This is because policy makers and judges oftentimes:
(1) serve the interests of lobbyists or special groups; and/or
(2) don't have a thorough understanding of an innovation and its foreseeable effects in the economy, technology, society, etc.