That may indeed be a factor, it's true that casual cruelty to people and animals doesn't seem to be particularly evil to people who are themselves suffering and struggling just to survive in a harsh environment where hardship and pain are everyday realities. But islam institutionalizes murder and cruelty as an offical intrument for converting the "infidel" world, and for keeping it's believers from accepting "heresies" such as Christianity.
Barbaric treatment of people by primitive, semi-civilized tribesmen is one thing, murder and torture as a deliberate policy of the educated and urbane clergy of an organized religious institution is something else. I believe the unspeakable cruelties practiced by the apostate medieval church were just as Satanically inspired as the cruelties of islam. But the church was reformed during the renaissance, and forced conversion was eventually proscribed both by the reformers and the Catholic church. Meanwhile, islam continues to force conversions and punish "infidels" by murder and persecution just as it has for 1400 years. This is also true to a lesser degree of some other false religions, but islam is the most notorious offender. I believe that all religions except Judaism and Christianity are Satanic in origin, but islam in particular seems to be his preferred instrument for persecution of the church and Judaism.