You are wrong on two levels here:
1) That Islam is only what Muslims do / Everything Muslims do is Islam
2) That all Muslims do barbaric stuff (which you are desperately trying to blame on Islam)
First of all, Islam is a set of beliefs based on a proper set of texts. If Muslims contradict those texts, what they are doing at that time is the opposite of Islam. Also, Muslims do plenty of (non-barbaric) stuff that is not Islam. Driving cars, eating Biryani or watching TV were never mentioned in Islamic text, yet Muslims do it. Does that make it Islam? No, it just makes it something Muslims (which are human beings, by the way) do.
Second, a very small amount of Muslims do the kinds of things you are talking about. The Majority is not involved in terrorism, warfare or politics. So, even if I was to go by your logic ('Islam is what Muslims do'), Islam is what the majority does i.e normal everyday lives, charity and praying a few times a day.