It is part of my job description to be offensive. I can, if I wish, make a joke hoping that Alex Salmond, now he is at the end of his political life, lays 20,000 fish eggs and dies. I can make a joke pointing out that David Cameron told off Sri Lanka for human rights abuses committed with weapons Britain sold it – like Ronald McDonald calling you a fat bastard.

The most I risk from saying such things is alienating a stranger. The same cannot be said of Mohammed Asghar. He is 70, and suffers from paranoid schizophrenia. He was sectioned under the Mental Health Act and admitted to a psychiatric hospital in Edinburgh. When they discharged him he went to Pakistan, perhaps to escape what he thought were the undue restrictions on his liberty. Before he had been there long – four years ago now, in 2010 – he was facing a death sentence for blasphemy.

There is no doubt I have offended many people. No doubt, also, that I have blasphemed. I sometimes try to offend as part of my routine – after all, the essence of humour, even in a child, is the effort to shock and surprise. I don’t advocate offending people purely for the sake of offence, but my own excuse is far weaker than Asghar’s: I do it for laughs, he does it because he is seriously mentally ill, and cannot help it.

Apparently Asghar claimed to be a prophet sent by God. As his Scottish doctor reports, if he said that it was definitely his psychosis talking. I cannot believe that the overwhelming majority of Muslims in Pakistan, Scotland or anywhere else think that he should be executed for this. Yet a small minority of vocal people do, and one of them – a police officer at the maximum security prison where he was being held – tried to murder Asghar last Thursday. The guard burst into his cell with a pistol and shot him in the back. He shot again, but missed, before being partially restrained by others. Then, as Asghar was being taken to hospital, the guard managed to get a last kick in, crying out that he wanted to “kill the blasphemer”.

There has been a recent epidemic of blasphemy charges in Pakistan. Forty-eight people have been killed before they could get to a trial. Many more are being prosecuted. It is difficult for a brave lawyer to defend a client, because if you repeat what the person is accused of saying, that is blasphemous too.

If you think I am joking, not long ago a prominent human rights lawyer representing an English professor accused of making a blasphemous Facebook post was shot dead – after the prosecution lawyers had threatened to kill him in front of a judge. A politician who discussed reforming the law on TV is now being prosecuted for what he said, and two others were assassinated (one by his own security guard, who is now lauded as a hero).

I realise that I am not the brave person who is walking the streets of Islamabad with a placard. But we need to stand up with the people who are brave enough to take this issue on.

To be critical is not the same as being anti-Islam – rather, it is to advocate for a rational, sensible interpretation of the religion. Islam does not allow for the execution of the insane; neither does it sanction those who, for their own reasons, take the law into their own hands. On the other hand, to fail to stand up for Asghar and others like him is to cede the ground to those who think it’s OK to kill people who say odd things.

This week Cameron is apparently planning to cede ground to people on the fringes of his own party, as he calls for Britain to renege on its obligations to the European Convention on Human Rights. Instead of moaning that there are too many human rights, Cameron should be focused on the very human plight of Mohammed Asghar.

Mohammad Asghar is being assisted by legal charity Reprieve, further information on his case can be found at www.reprieve.org.uk