And the truth is that Roe v. Wade is very much like Dred Scott and that those upholding it, like Taney upholding slavery, are biased in favor of what is ultimately an insupportable outcome and thesis. Killing the innnocent in the womb is as morally insupportable as slavery was.
Regardless of any similarity between Roe v. Wade and Dred Scott, however, it's likely no coincidence that Bush chose to mention the latter. Mentioning Dred Scott will likely not lose him any votes since few people understand that decision, much less support it. Mentioning Roe v. Wade, especially with an implication that he would work to overturn it, might gain him some votes but would likely lose him many more.