The reason Roe vs. Wade should be overturned is that it is the right of the citizens of individual states to make laws governing abortion. The majority opinion said that the 14th amendment prohibited states from banning abortion, but Rehnquist dissented, arguing that 36 states had laws restricting abortion that remained in force before and after the 14th amendment was ratified. There is no logical reason to assume that those who wrote and ratified the 14th amendment intended to prohibit citizens from exercising their rights to create laws restricting abortion. I think Emilio Garza sums it up the best:

"Two essential facts seem apparent: The Constitution says absolutely nothing about abortion and ... the long-standing traditions of American society have permitted abortion to be legally proscribed," he wrote. "Because the decision to permit or proscribe abortion is a political choice, I would allow the people of the state of Louisiana to decide this issue for themselves."

http://www.cbsnews.com/elements/2005...4_person.shtml

Roe vs. Wade did not legalize abortion, it prohibited states from banning abortion. With this decision, the Supreme Court set itself up for becoming an unelected nine-member dictatorship: making up meanings in the Constitution in order to fit their own personal convictions.