A leftist could make a respectable argument that even though Coakley was grievously out of bounds in the Amirault case the need for her vote on health care reform, filibuster prevention, and other issues is more important than the troubling decisions she made as a prosecutor. A leftist could also plausibly argue that when it comes to actually making criminal justice policy as a senator, Coakley isn't likely to be any worse than her opponent, and therefore she deserves support because she's more progressive on everything else.
But LeBlanc isn't arguing either of those positions. She's arguing something far more repugnant: She's conceding that the Amirault case was a travesty of justice, and that Coakley was wrong for her extraordinary efforts to keep Gerald Amiralut in prison. But she's then arguing that Coakley deserves a pass specifically for her actions in the Amirault case, anyway, because all prosecutors do it, and because it's what Coakley had to do to accumulate political power and move on to higher office.