Why Do We Think Slavery is Evil?

[Nope]

First of all, it is difficult to know without accurate information of what was really going on those millennia ago.

In those days, most of the 'slaves' may have been just as happy or happier as a 'slave' with room and board as long as they were treated well. Even if they were not 'slaves', and were working for someone, they may actually have been treated worse by an employer than a master and maybe not even have as good room and board as the slaves. They did not have unions in those days so, IMHO, six of one, half a dozen of the other.

Now days, how much better off is a minimum wage worker than a slave? Is slavery really gone?

There are photos online of slaves in the US who have scars from whippings. I would imagine that non Hebrew slaves in the bible had similar treatment. Humans are not usually good at having complete control over one another.

McDonald workers don't have to witness their children being sold or know that their wives or daughters have been raped. I agree working for minimum wage is horrible but it isn't as bad as slavery.