>1798, "method of printing from a plate," from French stéréotype (adj.) "printed by means of a solid plate of type," from Greek stereos "solid" (see stereo-) + French type "type" (see type (n.)). Meaning "a stereotype plate" is from 1817. Meaning "image perpetuated without change" is first recorded 1850, from the verb in this sense. Meaning "preconceived and oversimplified notion of characteristics typical of a person or group" is recorded from 1922 (Walter Lippmann, "Public Opinion").
>1804, "to cast a stereotype plate," from stereotype (n.). From 1819 in the figurative sense "fix firmly or unchangeably." By 1953 as "assign preconceived and oversimplified notion of characteristics typical of a person or group." Related: Stereotyped; stereotyping.
Stereotypes have reason for existing, they are a simplification of reality but a simplification of reality is still an imprint of it nonetheless. I provided this definition because it nicely demonstrates what it boils down to: the belief that humans are born as a clean slate. This sort of materialist notion that all of these things are just because of what people were forced into being. But due to indoctination to be in favour of equality they also go out of their way to deny even that, so you have this sort of cognitive dissonance: blacks were forced into becoming violent by the world around them (and as such are not to blame for being that way, they would do things differently if they could), but at the same time they actually aren't that way at all because they are equal to you in every single way.