I'm afraid it's a common synonym for slave for many people. It's not always a question of racism, it's a question of analogy. Noone would think of it as something happening today, you go back to those days with your mind. It's like you say "you're sadist like an inquisitor". That does not mean all religious people todays are disgusting people. English and american people feel probably more guilty using that word cause it's in their recent history compared to Europe where it happened during ancient history.