Complex sentence: All of the dissenting justices acknowledged that "the Constitution does not impose a duty to desegregate upon districts," if they have not practiced racial discrimination, but the dissenters also argued that the Constitution permits such desegregation even though it does not require it.
Split into simpler sentences: All of the dissenting justices acknowledged that "the Constitution does not impose a duty to desegregate upon districts," if the districts have not practiced racial discrimination. However, the dissenters argued that the Constitution permits such desegregation even though it does not require it.