"Tolerance always has limits - it cannot tolerate what is itself actively intolerant"

This quote by Sidney Hook speaks to the idea that tolerance is not an absolute idea. It is not something that can be used to any and all situations with no borders. Rather, tolerance has limits and those limitations are identified by what is actively intolerant. Simply put, if something is actively intolerant, then it can not be endured. This is since tolerance is a two-way street. It needs both celebrations to be tolerant of each other in order for it to be reliable. If one party is actively intolerant, then it is not possible for the other party to be tolerant. For that reason, tolerance constantly has limits and it can not endure what is itself actively intolerant.