The ∅ symbol (U+2205 in Unicode), even though it's inspired by, is not the same as the letter Ø (U+00D8 in Unicode), and has been, for almost a century already, the "correct" way to represent an empty set in mathematical notation (alongside {}).
That is the meaning everyone that does not primarily use the Northern European alphabet (aka most people in the world) assume it has.
Maybe suppress your instinctive outrage next time, or if you really need to be angry at something, at least direct it at the right place: the dead mathematician who proposed it [0]