The reason for opposing the rebuilding of the Temple by Rehum and his associates was that they believed the city of Jerusalem was rebellious and wicked. They feared that if the city was rebuilt and its walls finished, the Jews would not pay tribute, customs, or tolls, which would impair the royal revenue. Additionally, they mentioned that the city had a history of rebellion and sedition against kings and provinces, leading to its destruction in the past. All of these prove that Rehum and his associates were intolerant to the people of  Israel.