Harmless supernova fallacies are a class of arguments, usually a subspecies of false dichotomy or continuum fallacy, which can equally be used to argue that almost any physically real phenomenon--including a supernova--is harmless / manageable / safe / unimportant.

Bounded, therefore harmless: "A supernova isn't infinitely energetic--that would violate the laws of physics! Just wear a flame-retardant jumpsuit and you'll be fine." (All physical phenomena are finitely energetic; some are nonetheless energetic enough that a flame-retardant jumpsuit won't stop them. "Infinite or harmless" is a false dichotomy.)
Continuous, therefore harmless: "Temperature is continuous; there's no qualitative threshold where something becomes 'super' hot. We just need better versions of our existing heat-resistant materials, which is a well-understood engineering problem." (Direct instance of the standard continuum fallacy: the existence of a continuum of states between two points does not mean they are not distinct. Some temperatures, though not qualitatively distinct from lower temperatures, exceed what we can handle using methods that work for lower temperatures. "Quantity has a quality all of its own.")
Varying, therefore harmless: "A supernova wouldn't heat up all areas of the solar system to exactly the same temperature! It'll be hotter closer to the center, and cooler toward the outside. We just need to stay on a part of Earth that's further way from the Sun." (The temperatures near a supernova vary, but they are all quantitatively high enough to be far above the greatest manageable level; there is no nearby temperature low enough to form a survivable valley.)
Mundane, therefore harmless or straw superpower: "Contrary to what many non-astronomers seem to believe, a supernova can't burn hot enough to sear through time itself, so we'll be fine." (False dichotomy: the divine ability is not required for the phenomenon to be dangerous / non-survivable.)
Precedented, therefore harmless: "Really, we've already had supernovas around for a while: there are already devices that produce 'super' amounts of heat by fusing elements low in the periodic table, and they're called thermonuclear weapons. Society has proven well able to regulate existing thermonuclear weapons and prevent them from being acquired by terrorists; there's no reason the same shouldn't be true of supernovas." (Reference class tennis / noncentral fallacy / continuum fallacy: putting supernovas on a continuum with hydrogen bombs doesn't make them able to be handled by similar strategies, nor does finding a class such that it contains both supernovas and hydrogen bombs.)
Undefinable, therefore harmless: "What is 'heat', really? Somebody from Greenland might think 295 Kelvin was 'warm', somebody from the equator might consider the same weather 'cool'. And when exactly does a 'sun shining' become a 'supernova'? This whole idea seems ill-defined." (Someone finding it difficult to make exacting definitions about a physical process doesn't license the conclusion that the physical process is harmless. ^[1])

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It also happens that the distinction between the runaway process in a supernova and a sun shining is empirically sharp; but this is not why the argument is invalid--a super-hot ordinary fire can also be harmful even if we personally are having trouble defining "super" and "hot".

Harmless supernova fallacy