How did the Dred Scott case and Roe vs. Wade limit the ideal of liberty and justice for all?
It's important to understand the cultural context in which these decisions were made. The decision in Dred Scott did not limit the ideal of liberty and justice for all. In fact, the decision reaffirmed liberty and justice of property owners, by reaffirming the concept of property Rights.
As incomprehensible and as horrible as it is, the culture didn't consider slaves as people. They were just slaves. When the decision was made in Dred Scott, back in 1857, slaves were legally not considered to be citizens; they were instead legally considered to be "property." The decision underscored an owner's Right to "own" his or her property.
Fortunately, the concept of one person "owning" another finally went away with the Reconstruction Amendments being passed in the late 1860's. Only when slaves became citizens did liberty and justic truly prevail.
It is easier to make the case that Dred Scott limited this ideal than the case that Roe did.
Dred Scott clearly limited the idea of liberty and justice for all because it did not give liberty and justice to black people. In fact, it said that they could never expect liberty and justice because they could never be citizens.
To argue that Roe limits liberty and justice, you have to argue that a fetus is a human being. If the fetus is alive, then Roe limits its liberty and denies it justice by making a ban on abortion illegal. It, in effect, tells people that it is legal to kill the fetus just as Dred Scott said that it was legal to deprive black people of their freedom.