(1)Even if we accept that they may have been treated better (which I don't) , that does not address the immorality of claiming to "own" another. The fact that the Bible didn't point this out supports the idea that humans often mistake their own attitudes for divine commands. Further, the Bible says slavery a bad thing if your slave is Hebrew. The racial or religious identity of a slave doesn't impact the immorality of the institution. (2) "Allowed" = "supported". Either a righteous deity condemns the immoral practice or not. If mixing fabrics is called out as an abomination, the fact the slavery is not equates to support.