Taney gets a bad rap, IMHO. Scott was decided 7-2, and clearly grounded in the Constitution and its history. Roe was not. The analogy is a bad one.
ML/NJ
I think the Dred Scott Decision is used because it retrospect it is so blatantly immoral. However, purely in terms of horrible decisions, I think it makes far more sense to compare Roe to Plessy v. Ferguson (which is also the only SCOTUS decision which a future SCOTUS subsequently overturned, Dred Scott was made moot by post-Civil War amendments).