Critical thinking is essential for a philosopher because it allows you to see what masses are not able to.
For example, Hitler with his Propaganda controlled the masses. His Propaganda worked on the fear, hate for other races and emotions of masses. But there were still a lot of people who were not controlled by Hitler's propoganda and those people were, who were able to think critically.
Hitler believed masses to be stupid and that's why he uses short slogans in his propoganda. He appealed to emotions of people rather than reason.
Hitler thought thag three kind of people existed.
People who believed everything they read and heard. Hitler thought that these were the majority of people in masses.
People who have gone to extreme and have ceased to believe in anything. People like these will not believe in anything.
People who examine critically what they read and hear. These were the smallest in number. As Hitler write in His book My Struggles, "It consists of the minds with real mental subtlety, whom natural gifts and education have taught to think independently, who try to form their own judgment on all things, and who subject everything they read to a thorough examination and further development of their own. They will not look at a newspaper without always collaborating in their minds, and the writer has no easy time of it."
Hitler said that these third type of people were evil and we needed to defend our childrens and family from the influenced of these kind of people.
You may have heard that Hitler was great st speech but in reality, he spoke only what appealed to emotions of masses.
All critical thinker may not have been philosophers but all philosophers were able to think critically.