I find this criticism not well founded. If I told you "In the plane, the inner angles of a triangle always add up to 180°, because...", would you be justified t

I find this criticism not well founded. If I told you "In the plane, the inner angles of a triangle always add up to 180°, because...", would you be justified to interrupt me at that point saying "your conclusion shouldn't be your first axiom"? (answer 'yes' if you want to be fun at parties).