How would John's baptism have offended a Jew's national pride?

According to Baptism—Pagan or Jewish? by Ceil Rosen the Jews in that period were very familiar with the act of baptism. Gentile converts to Judaism were required to be circumcised, baptized and bring a sacrifice to the temple. This baptism was considered a once for all baptism that cleansed the Gentile's soul of the sin of their worship of idols allowing them to be brought under the covenant of circumcision. The baptism John preached was also a once for all baptism to cleanse the Jewish soul of their sins. It is this idea that the chosen nation of God would need the same spiritual cleansing as a Gentile that would offend the Jews, especially the religious leaders.