Perhaps, the key to attack him isn't abortion, but civil rights. Roberts was one of Reagan's henchmen  who systematically sought to overturn all types of Civil Rights laws and legislation, from affirmative action to Title IX. This article hints that his propensity to rewrite exisiting legal statutes early in his carrer may make him unfit for the bench now.

Now if we can just get around his defense that 'he was just working for the man, and those weren't necessarily HIS views...'