Re: Sigh...
It comes about because teaching about historical US slavery is frequently the only time slavery is ever mentioned in US education from ages 0-18. So any time anyone mentions "slave" the only point of reference almost any USian has is "chained black person". So when they encounter "slave" as a term of art in industry, they cannot comprehend that it could be anything other than endorsing/belittling/making fun of the history of slavery in the US.