Why was it a long time before people began to object slavery?

This has a very long answer. You could research this for years about different subjects that pertain to this, and still not learn everything there is to know about it. Ethics, Social constructs, Culture, The economics of necessity, etc. Throughout history there always was and will be people opposed to slavery and even fight against it, and there always was and will be people who use it for their own benefit. whether your talking about African American slaves in America, or barbarian slaves in ancient Rome, there were always people who were for AND against it. What seems to be the case, in an objective standpoint, is that love usually triumphs over hate, because working together is what makes peaceful, prosperous life possible along with technological advancements.