Why should we treat women prisoners differently? That has been the response from a significant number of people in the wake of the decision not to build HMP Inverclyde near Greenock.

Comments online on articles I've written, reaction on social media and callers to radio phone-ins have all featured variations on the theme: women who don't want to do the time shouldn't have done the crime.

There are various misunderstandings here. The most obvious one is that it isn't women offenders who are saying that they don't want to be sent to a 350-capacity prison 26 miles west of Glasgow.

Of course if you asked them, I'm quite certain most would say no. But it is penal experts, charities working with women who break the law, and policy makers who decided this is not what we want.

Some argue that women offenders are already treated differently from male ones. It used to be that they tended to be sentenced to prison more readily, given jail terms for lesser offences, or incarcerated after committing fewer crimes.

Baroness Jean Corston's 2007 report for the UK Government on women's offending pointed out that more women are remanded in custody than men, while 37% of adult women sent to prison between 1992 and 2002 were jailed for a first offence, more than double the rate for men.

But sentencing is possibly more balanced now. When former Lord Advocate Elish Angiolini's commission on women offenders reported in 2012, it found no evidence that women were treated more harshly than men. In fact they were slightly less likely to receive a prison sentence than their male counterparts for an equivalent crime.

However the Commission concluded that it was right for women to have different treatment. The Corston report reached the same conclusion.

There are many reasons for this. Women are different from men. Prison is harder on them in many ways - the mental health problems caused for those separated from children are not the same as for men. For one thing, while a child whose father is jailed is usually looked after by their mother, if the mother is jailed the reverse does not apply, and the arrangements for their care can add an additional level of anxiety or even punishment.

Levels of mental health problems in women's jails are known to be sky high. Women offenders tend to have drug problems and histories of abuse.

This sounds like special pleading, and there are plenty of male prisoners with mental health or addiction problems or troubled childhoods. There is certainly a case for more enlightened treatment of men in jail too.

But the priority given to reforming women's prisons, dates back decades - Henry McLeish pledged to halve the number of women in Cornton Vale in 1998.

This is partly for the benefit of the inmates, but also recognises the devastating social cost of imprisoning women. Reoffending costs tens of thousands of pounds, traumatising children - who have done no wrong themselves - has a lifelong cost. The majority of women offenders are not a real danger to the public and alternatives disposals such as smaller units, mentoring of female offenders and community sentencing have been shown to be more effective.

Despite widespread agreement about this, the move towards such alternatives has been glacial.

The confusion over whether it is 'just' to treat women differently must be partly the reason. But may be just in everyone's best interests.