Roe is Judicial Activism
Blackmun took copious notes and going through his papers Historians (Jeffrey Rose, Michael Kinsley, William Saletan) have agreed, "Blackmun’s [Supreme Court] papers vindicate every indictment of Roe: invention, overreach, arbitrariness, textual indifference"
Edward Lazarus, Blackmun's law clerk who "loved [Blackmun] like a grandfather," wrote: "As a matter of constitutional interpretation and judicial method, Roe borders on the indefensible.... Justice Blackmun's opinion provides essentially no reasoning in support of its holding. And in the almost 30 years since Roe's announcement, no one has produced a convincing defense of Roe on its own terms."
A progressive judge with a God complex decided that the laws of the land doesn't matter: he wanted to protect abortion at the federal level, so legislated from the bench to do it. Thus, some people who oppose Roe do it for personal beliefs, others have a completely grounded legal (rule-of-law) reason to disagree with the ruling. I'm in the latter camp.