Perhaps so, but I would suggest that the pro-life crowd would do well to support it.
First of all, it would be an immense improvement over the status quo, protecting many children who at the moment have no protection even after they're born (if a child is born during an attempted abortion, doctors will often kill it even though it's completely out of the mother's body).
Secondly, it would split the pro-choice people into those who believe that it's okay to kill a blob of flesh but not a baby, versus those who think even fully formed and delivered babies are disposable. The latter group try to conceal their true agenda, but splitting off the former group would expose them.
Thirdly, it would establish a pretty strong "ratchet" that can only move in one direction. A pro-choice person may be able to argue, for awhile, that an eigteen-week fetus is just a blob of cells even though a 21-week fetus is a baby, but as techniques for rescuing premature infants improve, the line will get pushed earlier and earlier. Until doctors can rescue 18-week fetuses, the "blob of cells" argument might hold some water, but once they can manage such rescues, that argument will be destroyed forever.
Finally, it would help reveal the true nature of public opinion. While it is true that the vast majority of people favor allowing abortion in at least some circumstances, very few think it should be allowed as broadly as it is today. If someone feels that most abortions should be restricted, but feels more strongly about protecting those few that he feels shouldn't be, such a person would be in the "pro-choice" camp in today's climate, but would be in the "pro-life" camp if said camp focused on restricting those abortions that most people feel should be restricted.