That you can find some examples of a tiny minority slaves doing some highly-skilled jobs does not contradict the statement that it's unlikely that slavery as an institution would be compatible with a modern economy, even ignoring the obvious moral evil it represents.

Also, just by the way, we ought to be able to talk without implying that other people have "those tendencies". There is simply no reasonable way a comment about the structure of an industrialized economy can be constructed as "having those tendencies". Appending "slavery = bad" to every comment is tiresome, there is such a thing as context.