Islam is causing particular problems in the world at the moment. But other religions have also been the excuse for destruction and torment, for example in Europe at the time of the Inquisition, or more recently in Northern Ireland, North Uganda, Kashmir or Punjab. Religious leaders would argue that religion was not the cause of the suffering, only the excuse, and that their religion had been used and abused by rulers for ulterior motives. This may be so, but it is difficult to imagine that those leaders would have found it so easy to inspire savage acts in the name of humanism.
There are many excuses besides religion that can be used by rulers bent on destruction. Indeed, of the three greatest mass murderers of the last century, two (Stalin and Mao) were atheists, and the third (Hitler) did not act in the name of religion. But their killings were not carried out in the name of atheism. They were carried out in the name of barbarous philosophies that subsumed the rights of individuals beneath the objective of a supposed greater common good. Those philosophies have been shown to be an aberration, and for the most part abandoned. Religion remains the greatest motive for abuse that has yet to be challenged.
It is hard to see how one could defend against the proposition that religion does more harm than good. Yes, good is done in the name of religion, just as evil is done. But if you contend that religion is merely an excuse for evil, can you defend the proposition that it is always the cause of good? Would all those people working for religious charities not carry out their activities if there were no god? Are they motivated by the word of god, or by their humanity? And even if one attributes all the good done in the name of religion to that religion, have those acts ever done more than mitigate the impact of the disasters to which they were attending? Unless religious charities can protect all people from harm, the balance sheet of religious impact will always be in the red.
And every tragedy like that in London last week raises again the question that theologians of all religions have never managed to answer: how does a loving and all-powerful god (or gods) allow (or cause) events like these to occur (the so-called "problem of evil"). It is nothing to do with free will - those who died in these disasters did not choose a course of events that they knew would lead to their death. Their death was something that was done to them. Nor can you use one of the great excuses of religion - that the people whose lives were ended so abruptly were either being punished for their wrongdoing, or (the other side of that coin) were so loved by their god(s) that they were being called into His (/Her/Their) presence. People of all (and no) religions were killed. Doubtless many of those people led blameless lives, but it is unlikely that none of them had ever done something that would be considered wrong in the eyes of their god(s). Without these excuses, the devout fall back on mysteries - that it is all part of their god's plan, which mortals cannot understand. That is tantamount to saying "Faith outweighs rational thought, so there must have been a reason, even if I can't see it." It's not much of an answer.
The problem of evil does not disprove the existence of gods. It disproves the existence of loving, all-powerful gods. But if we accept that any god is either not loving or not all-powerful (or perhaps even neither), our reasons to follow their teaching are significantly diminished.
None of this denies people's rights to believe whatever they like. It is an important part of a free society that people should have the right to their beliefs, provided that those beliefs do not result in a course of action that harms others. But it does raise the question of whether we should have state-sponsored religious education. Children (and adults) need an education in ethics and morality, not in stories about wine and water or mountains and prophets. We can learn about moral and ethical issues from the various religions and their stories. We can gain a deeper knowledge by understanding the teachings of many religions. But we can also learn from history and from our own experiences. And the understanding that comes from personal experience is more important than the teachings of religion or the study of history. People should follow a course of action because they know and understand it to be the right course, not because a higher power has said that it is so.
Religion will not disappear tomorrow, or in a hundred years. But if we take a rational approach to moral and ethical education, we can begin to diminish religions' powers. If we diminish those powers, we reduce the pool of blind faith from which evil often draws. And one can only hope that one day belief in gods will come to seem as quaint and absurd as belief in fairies or Father Christmas.