Do you feel yourself sometimes tempted to evils that a healthy mind rejects? Do you feel yourself as well sometimes tempted to outstanding goodness that your timid and callous mind rejects? Do you ask yourself how, how, how can people do some of the horrors they do in our world? Do you wonder as well how people find the incredible strength and courage by which they do such valorous and compassionate acts of service and sacrifice?
I've always chosen to believe that people are themselves able to do great evil and great good, and that demons and angels are just foolish rationalizations for such things. But I must here confess to occasional pondering on such matters. What say you all?
Answer: We humans have both: the potential for good and evil, and the free-will to choose which path to follow. Whether it is our own self which urges us to do great good or horrific evil, or whether our minds are prompted by suggestions from other humans or supernatural beings, for all sane thinking people, the responsibility for the choice they make and their actions rests with themselves.
From the Islamic perspective, we believe in the existence of angels and dJinns. We also know that angels do guard and supplement good efforts by God's command. We also believe in the existence of good and bad dJinns, but that they can only suggest ideas, and that they do not have any real power over us. We ultimately are responsible for our choices.
Consider Surah Naas (Chapter 114):
1 Say: I seek refuge in the Lord of humankind,
2 The King of humankind,
3 The God of humankind,
4 From the evil of the sneaking whisperer,
5 Who whispereth in the hearts of humankind,
6 Of the jinn and of humankind.
We also believe in pre-destiny: that all that happens is already decreed. Consider the following verses: Surah Hadeed (Chapter 57):
22 No misfortune can happen on earth or in your souls but is recorded in a decree before We bring it into existence: That is truly easy for Allah.
23 In order that ye may not despair over matters that pass you by, nor exult over favours bestowed upon you. For Allah loveth not any vainglorious boaster,-
Coming back to the original point, the ability to discern between right and wrong, consider the following verses from Surah Shams (Chapter 91):
7 And the soul and Him Who made it perfect,
8 Then He inspired it to understand what is right and wrong for it;
9 He will indeed be successful who purifies it,
10 And he will indeed fail who corrupts it.
As for the Syrian example you raised, well just as we are individually capable of all things, so are we collectively capable of good and evil. Its sad, but history simply keeps repeating itself. Humankind simply refuses to learn.