Complex sentence: Discussion of how people perceive scientists as being arrogant, despite religionists never being able to say "I don't know", whereas "we just don't know" is the default position of a scientist until something can be proven.
Split into simpler sentences: Discussion of how people perceive scientists as being arrogant, despite religionists never being able to say "I don't know". Although, "we just don't know" is the default position, until something can be proven.