Nowhere in Quran it commands to take slaves, rather it repeatedly calls for freeing of them. As for the reason Quran doesn't forbid slavery: 1)Slavery was an indispensable practise until Late Modern Period throughout the entire world, so it would be nigh impossible to force it on many. Think of it as Putin trying to ban vodka for being harmful. Would be funny, wouldn't it? 2)Slaves during Mohammed's era were seen as servants, a part of the family, and not disposable workforce as it was the case in the rest of the world. Most were content with their lives and had nowhere else to go, so to abolish slavery would be unwelcome by both sides. Both Muslims and Christians(Europeans) have done terrible things in the past. But the blame has always been on their own, not their scriptures'. If you want to criticize Muslims then go ahead, i already beat you to it every single day. Just don't correlate their moronic behavior with Quran.