This ad was put out by Kelly Services, a temporary staffing agency, in 1971.
Let's, for a moment, bypass the creepy, "Mad Men"-esque vibes here and focus on some of the words. The basic proposition here is that temp workers are better than full-time staffers because a) they're cheaper and b) they're completely expendable.
This is a message that hasn't been lost on corporate America, which has been hiring temp workers at record rates since the 2007-2009 recession. And this 40-year-old premise hasn't changed either — it's way easier to exploit someone when they've got no leverage.
Clarification: A (surprising) number of you in the comments section seem to have worked for Kelly Staffing Services and had positive experiences. My intention isn't to comment on the company at all — just this ad and the premise behind it, which still applies to how many companies think about and treat temporary workers.