We have seen Pakistan's blasphemy laws used as a blunt instrument against Christians, usually by people with a personal grudge. There are even some Muslims who feel that the central claims of Christianity are an 'insult to Islam', because if the New Testament as we have it today is true, then various claims of the Qur'an are, it follows, false. If Jesus is the eternal Son of God and not just a human prophet, then the Qur'an is wrong when it claims he is not. If Jesus died on the cross, then it follows that the Qur'an is wrong. And if the Qur'an is wrong, then it is not the word of God. At this point the sensible thing to do would be for us to reason together - but it has always been easier to use violence, as centuries of history have taught. And it's not just Muslims, it is found in Christendom as well, Roman Catholics against Protestants and State Churches against Nonconformists. The book of Acts records cases where Jewish and pagan leaders used violence in an attempt to silence opposition - it is always easier to do that than it is to allow true religious freedom.
Not that there is not such a thing as defaming a religion. The first example that comes to mind is the infamous 'Blood Libel" against the Jews, first invented in the Middle Ages. The Blood Libel is the idea that the blood of a Gentile child is part of the ingredients of the Passover matzos - a claim that is patently ridiculous in the face of the prohibition against eating blood that all Jews observe! There have been many lies told about religious groups with the intention of creating hatred against them, and there still are. A few examples that come to mind are the ancient claims that Christians were cannibals (probably based on a misunderstanding of the Eucharist) and committed incest (probably misunderstanding the Christian practice of calling one another 'Brother' and 'Sister'. Paul says that the Apostles had the right to have "a sister as wife', meaning freedom to marry a Christian woman). Modern claims that come to mind include one saying that all Muslim men have to kill a non-Muslim to be considered truly men, and that human sacrifices take place in Mormon temples. These lies really are defamation, and should be punished first of all by society - we should refuse to listen to them and treat those who maliciously repeat such claims as the troublemakers they are.
But to restrain religious freedom - and as an inheritor of the traditions of English Nonconformity wish to extend that freedom as far as possible - because one religious group is upset by another religious group's claims is frankly tyrannical. I do not like the claims of Islam about Jesus, God and the Bible - but they have the right to teach them, and I have the right to challenge them. I find the teachings of Mormonism about God frankly pagan - but I am very glad that they have the freedom to build their temples, as I have the right to give good and true reasons why Mormonism is not Christianity. My feelings - and your feelings - must not be made the basis of restrictive laws. Christianity is not spread by the sword in any way, and the truth will be triumphant over error in a fair contest.