Religions start all the wars ... except for the ones that aren't started by religions. After all, lots of wars are just territory-grabs, and neighboring tribes did the same to each other long before even Judaism came on the scene. (I've been tempted to answer that governments start all wars and therefore we should become anarchists, just as a tongue-in-cheek response. Relatively few wars happen without state sponsorship, after all; should all the governments be pressured to disband?) On a more serious note, I think hatred, pride, and greed explain more wars than any other factors. For that reason, whatever encourages love, humility, and generosity will promote peace.
The religious are more violent than the non-religious ... except for all the atheist mass-atrocities of the 20th century. I see a lot of people lining up to criticize their favorite opponents, selectively reading both history and current events to make their side appear to be the good guys and those who disagree appear to be the bad guys. The dissenters are portrayed as not only wrong but also dangerous.
Is it accurate to define firm belief as inherently dangerous? For example, is the belief that you should love your neighbor inherently dangerous? How about the belief that you should kill people who will not convert? If those two beliefs were held equally firmly, would they be equally likely to result in harm to the neighbor? One more belief might be worth mentioning here. If you consider the deaths of people of all religions under the communist regimes of the 20th century, then the belief that "Religion is dangerous" may deserve a place among the destructive beliefs that cause violence when someone holds it too firmly.
As we have seen, it is careless to label all firm belief as "dangerous." If the word "dangerous" has any meaning at all, there must be some risk of harm behind it. Where the content of the belief does not endorse the use of force, and if the larger framework in which the belief is held does not endorse spreading beliefs by force, then there is no risk of danger, no matter how many people hold a belief firmly and unswervingly.
Is fundamentalism inherently dangerous? The most fundamentalist Christian that I know spends her time loving her family and helping her neighbors. That's what you actually get from adhering to Jesus' teachings and example. "Fundamentalism" is a label without a particular content; it basically means there is, somewhere, something on which you aren't willing to compromise. If the thing you won't compromise about is love of neighbor, we could use more fundamentalists.