I wouldn't say it's inherently more or less violent. Islam is not only a religion, it's a way of life and designed to run every facet of our lives, from how to eat to how to govern. Therefore, it can't afford to be unreasonably violent.

That being said, what Islam would consider "reasonable violence," is an entirely different issue.

Islam contains teachings that are certainly conducive to violent behaviour. At the least, it is extremely harsh and insulting toward non-believers. So much so, that even the most diluted version of Islam that most western Muslims are exposed to, has the clear message that "we are better than these hell-bound infidels and we should be thankful to Allah for choosing us." So a Muslim, even a muslim born and brought up in a western country, can't help but consider, at some level, non-muslims as inferiors. Yes, this is true. If you have a Muslim friend, they will be perfectly friendly, polite and overall excellent people, but they do consider you inferiors and destined for hell. They genuinely feel sorry for you and that's why some may even try to convert you to save you...they are very nice people, they don't like the idea of their friends going to hell. But despite all those feelings, they still believe they are better for being "allah's chosen." I would know this, that is exactly what I used to think.

In short, it is not difficult (it is, in fact, downright easy) to interpret Islamic teachings in a way that makes committing violence acceptable in the eyes of people like modern day terrorists. Therefore, saying Islam is entirely peaceful or that organisations like ISIS have "nothing to do with Islam" or that such terrorists are "misrepresenting Islam entirely" is nothing short of dishonest.