According to Karl Popper, this ability of scientific statements to expose the condition of its own falsification is the essential feature of ‘true science’. Pseudosciences, on the contrary, do not expose themselves like this. Rather, it would ‘explain out’ the situations that have emerged contrary to their initial statement. Thus, pseudosciences will not let itself be refuted by objective evidence, but would rather ‘somersault’ with adhoc or posthoc explanations.
Convinced of the ‘openness of science’ and the contribution of its openness to the progress of mankind, Popper wrote a two-volume book titled “Open society and its enemies”. In this book-series, Popper makes a statement widely known as the ‘Paradox of tolerance’. He states that unlimited tolerance must lead to the disappearance of tolerance.
“If we extend unlimited tolerance even to those who are intolerant, if we are not prepared to defend a tolerant society against the onslaught of the intolerant, then the tolerant will be destroyed, and tolerance with them”. Many leading social commentators agree to this idea. For instance, John Rawls, who propounded an influential theory of justice, state that while as a general principle a just society should be tolerant to the intolerant, the extend of tolerance is NOT infinite. “While an intolerant sect does not itself have title to complain of intolerance, its freedom should be restricted only when the tolerant sincerely and with reason believe that their own security and that of the institutions of liberty are in danger”
I think the Islamic proselytizer Zakir Naik is a test case to apply this principle.