How would John’s baptism have offended a Jew’s national pride? Well to the practicing Jew the baptism of John would have taken alot of humility because as was described: "the antecedent for John's baptism is the first century practice of Jewish proselyte baptism, a ritual bath by which a Gentile convert to Judaism was cleansed from moral and religious impurity". They would have to say in their hearts that what they beleived was wrong and repent from it. They would have been outcasts from their own people.
Who welcomed John’s baptism? It seems the regular everyday Jew who was not learned in the law and religious communities of the day and were seeking God.
Who resisted it? The Pharisees, Sadducee, religoious leaders of the day and the lawgivers. They thought themselves holier than thou and no in need of repentance.
Why? They felt they kept the law and were outwardly righteous and were not right inwardly.