If I am willing to work for less than someone else, it is wrong to insult me for that with terms such as "scab". I own my labor and other people own theirs. I would not take a job unless it were the best available to me.
"Scab" is a hate term that has been used to justify violence against so-called scabs. Epithets for gays have served a similar purpose in the past and are now considered to say more about the speaker than the target.