Why did opponents of the civil rights act of 1964 used fillybuster to try to block its passage

To pass a civil rights bill in 1964, the Senate proponents of that bill developed a three-part strategy. First, Majority Leader Mike Mansfield maneuvered the bill away from the Judiciary Committee and made it the Senate's pending business. Second, a bipartisan legislative team of senators and staff, led by Majority Whip Hubert Humphrey and Minority Whip Thomas Kuchel, developed a plan to defeat a well-organized filibuster. Finally, they enlisted the aid of Minority Leader Everett Dirksen. Only Dirksen could provide the Republican votes needed to invoke cloture and bring about passage of the bill. "The bill can't pass unless you get Ev Dirksen," President Lyndon Johnson told Hubert Humphrey. "You get in there to see Dirksen. You drink with Dirksen! You talk with Dirksen. You listen to Dirksen."

In an era when there were many factional divisions within both political parties, the biggest headaches for Democratic leader Mike Mansfield often came not from Republicans but from the conservative bloc of his own party caucus. The filibuster that threatened to derail the civil rights bill in 1964 was not led by the opposition party, but by an opposing faction within the majority party. To invoke cloture on the civil rights bill, Democratic proponents of the bill needed strong Republican support. If the bipartisan team could gain the support of Dirksen, a small-government conservative from Illinois, they might win over other conservatives.