You may call them "slaves" using a more modern lens, sure, but of course different times and places require a relativistic shift in order to understand things as a local living in the time would have understood them. You are right that we can't ask someone living in that time/place if they thought themselves a slave, or whether they thought it was good or bad to be one. However, we do know enough about ancient Egypt to at least fill in some context that minimally casts doubt on the notion that they saw themselves as unwilling slave laborers.
A good thought exercise is to consider: What are some things you are compelled to do today by your own government or economic limitations? How many of those things could you imagine a different and presumably more wealthy/capable future society would consider abhorrent enough to think you a "slave" or something like one?
A good thought exercise is to consider: What are some things you are compelled to do today by your own government or economic limitations? How many of those things could you imagine a different and presumably more wealthy/capable future society would consider abhorrent enough to think you a "slave" or something like one?