It wasn't so long ago that the Catholic Church were the ones who were the religious extremists. How many deaths have they been responsible in the name of god? How many armies went to war while both sides were blessed by the church? You have to remember what the church has been responsible for over the years. Look at the witch trials 100 000 people killed because the church accused them of witchcraft. There always has been religious extremists and there always will be. The world would be a much better place if religion did not exist.
the world would be a better place if oil didn't exist, if money didn't exist, if drugs didn't exist, if marriages didn't exist, if child custody didn't exist, if guns & bombs didn't exist, if racial intolerance didn't exist, if people with different beliefs to our own didn't exist, if
humans didn't exist..... there will always be extremists of ANY cause. You can try to ignore it as much as you like, but bottom line is, over 80 million people were killed in 2 world wars, and thousands more die every year from non-religious motivated violence, not because of religion, but from greed, intolerance and the quest for power. Hell in some countries people turn to violence, riot and even kill each other when their soccer team loses a game...
Violence is in our nature.... some more than others. Fortunately the majority of us have enough self-control to contain it. And unfortunately there will always be extremists of many causes (religious and non-religious), who can't. Take away religion, and the same wars will still happen, there will simply be another 'cause' used as an excuse to justify the actions.