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MetalGreymon Completely subjective, not just largely. Whether it's a valid view to hold or not is separate and up for debate, but definitely entirely subjective.
For example, not all slaves were mistreated. In fact, histories are
filled with accounts of slaves being treated very well and living objectively very pleasant lives, often a lot better than common peasantry since they were living among the upper class of society who were slave owners. But there is a spectrum to human behavior in all cases, and the problem that arose with slavery was that because slaves were not considered citizens they had no rights until declared freemen. Which meant that,
if their master's chose to abuse them and never free them there was really not much if anything they could do about it. At least, aside from kill their master. (Which happened
a lot to cruel slave owners in history too, and in some cases was one of the dominoes that lead to the toppling of entire empires.)
So free people realized that some of these enslaved people were being treated in terrible ways and living incredibly terrible lives and the entire concept of slavery becomes immoral, regardless of there being good slaves or not. It's much simpler to ban something than to regulate it, so of course governments will tend to support those kinds of ideas and leverage them... It's a complicated thing. I wouldn't necessarily support slavery in the modern day, but I can't realistically say that it was universally bad and it's obvious that not everyone in all of history has felt that way either.
Also, on the subject of plants, I echo that sentiment. I think people just disregard the lives of plants because they are so different from us, not that their lives and experiences are any less valid.