Jacob Appel: Allowing a manslaughter defence brings risk of anarchy

Law-abiding Americans on both sides of the abortion debate were horrified when George Tiller was shot dead outside his church. They should be equally disturbed should anti-abortion extremist Scott Roeder be allowed to present a voluntary manslaughter defence at his trial for the crime. Should this decision stand, the defendant can avoid a murder conviction if he proves he had "an unreasonable but honest belief that circumstances existed that justified deadly force".

Allowing this defence significantly increases the threat to other abortion providers. It also has disturbing implications for the prosecution of a wide range of suspects – from animal rights extremists to al-Qa'ida terrorists.

Judge Warren Wilbert had already rejected efforts by Roeder to plead "necessity", a legal argument that would have excused his acts if he could establish that they were required to save the lives of unborn children. In doing so, Wilbert cited a Kansas Supreme Court ruling in another case, which warned that allowing the necessity defence in abortion cases would "not only lead to chaos, but would be tantamount to sanctioning anarchy". Now, by ruling that Roeder may plead what amounts to "guilty with a good explanation", Wilbert has sanctioned precisely such anarchy.

A murder conviction will likely place Roeder in prison for life. In contrast, a manslaughter conviction would lead to a roughly five-year sentence. For those extremists who believe that they are killing to save innocent babies, losing five years of freedom may appear trivial. In short, Wilbert's ruling lowers the bar to violence.

The decision has implications far beyond abortion. The militants who flew jetliners into the World Trade Centre presumably also believed their actions justified, as does the Animal Liberation Front when it murders researchers to save monkeys. By this approach, trials about violence would become public hearings on abortion or foreign policy or research ethics.

Trial judges in the US have two goals: to serve justice and to avoid being overturned by an appellate court. Most likely, Judge Wilbert has given Roeder's defence team considerable latitude at present so that Roeder will have fewer grounds for appeal if convicted. As a method of trial management, that makes practical sense. Unfortunately, this approach threatens to transform the trial of Scott Roeder into a hearing on abortion and even a broad exploration of American social values, a subject for which an obscure Kansas courtroom is poorly suited.

Dr Appel is a writer and bioethicist who practises medicine and healthcare law in New York