does religion cause terrorism?

It's a common charge these days. Nobel Prize winning Physicist and atheist Stephen Weinberg said: "for good people to do evil things, that takes religion." And this atheist certainly seems to thinks so: "we see religion regularly used for war, mass murder, terrorism, and even genocide"

Are there any facts on the subject?

It turns out that there are. Here are the results of a few studies that have been done

• From this textbook: "Suicide terrorism is not caused by religion. ..... Suicide terrorists are motivated mainly by political goals ..... Their 'martyrdom' is, however, frequently legitimized and glorified by reference to religious ideas and values. ..... Extremist ideologies of a secular or religious nature are at least an intermediate cause of terrorism, although people usually adopt such extremist ideologies as a consequence of more fundamental political or personal reasons." This book lists a whole swag of the major identified causes of terrorism, and they are almost exclusively political in nature.
• From an international conference on terrorism: "Religion is seldom the only cause of terrorism. The scholars agreed that while religion has been a major factor in recent acts of terrorism, it is seldom the only one. ..... usually ‘political and economic grievances are primary causes or catalysts, and religion becomes a means to legitimate and mobilize’. .... Religion can contribute to a ‘culture of violence’. ...... ‘religion is seldom the problem, but the role of religion can be problematic’"
• From this article: "Credible researchers agree that "religion" neither causes nor explains suicide terrorism. ..... religious rhetoric may help persuade attackers that their cause is either necessary or noble, and that glorifies or renames suicide as martyrdom, but it does not explain why suicide attackers choose that particular tactic."
• And from this article: "People choose terrorism when they are trying to right what they perceive to be a social or political or historical wrong—when they have been stripped of their land or rights, or denied these."

It seems clear then that, yes, religious extremists are the source of some terrorism, and religious belief does sometimes support terrorism primarily motivated by political causes, but, no, religion is not the major source of terrorism. Politics, inequality, injustice, and ethnic/national grievances seem to be the main causes.