The biggest challenge facing the mentally ill is the lack of access to urgently needed treatment. It is supposed to be one of the government's top three medical priorities. Rightly so. No other disease affects so many: an estimated one in six people of working age suffers some form of mental condition ranging from depression through disabling anxiety disorders to schizophrenia. And yet mental health funds still get diverted to more powerful medical specialties, leaving community mental health teams over-stretched and undermanned. No wonder the mental health lobby talks about the government's draft bill as a "once-in-a-generation opportunity to drive mental health up the political and social agenda". So why this week was there so much opposition from the lobby to the newly redrafted bill?

Simple. The main driver behind the bill is not the needs of the mentally ill but a desire to appease a media-misinspired public concern with the risks that mental patients pose. Statistically you are 20 times more likely to be killed by a sane person than an insane one. By far the biggest threat posed by mentally ill patients is to themselves, with more than 1,000 committing suicide every year. Yet public fears over the threat posed by a tiny number of people with dangerous and severe personality disorder (DSPD), formally known as psychopaths, still prompts ministers to respond. It is six years since they promised to close the loophole exposed by Michael Stone's murderous attack on the Russell family. He had not been detained earlier because his DSPD was deemed untreatable.

An earlier version of the bill published in 2002 was withdrawn following opposition of the Mental Health Alliance, a powerful 60-strong group of professional and patient bodies concerned by its civil rights implications. It allowed detention of DPSD patients even if they had not committed an offence and had no prospect of cure. If it is right to detain dangerous people who are treatable, why is it wrong to detain them when they are untreatable? There is an important difference. For the first, rehabilitation and release offers hope, where there is none for the second. Indeterminate detention could not be more serious, but ministers have belatedly recognised this principle in their redrafting. Time for the lobby to reciprocate. It opposes compulsory community treatment orders, yet we have moved a long way down the "hospital without walls" road since the idea was first raised 20 years ago. Ministers have made concessions here too. Time for MPs to require the lobby to justify itself.