Judging before you know someone?

This question largely came about due to ignorance. I was reviewing old questions I had asked and came across a comment on one of my q’s that really bothered and hurt me. The q was in regards to info about immigrating, the comment was “no way we dont need racist people” im curious as to what leads people to stereo type or judge others? Purely on the basis of me being from the western world and that im caucasion I was slandered. I didnt feel it necessary to mention that im going there to marry my gorgeous black moroccan fiancee, or that the vast majority of people I associate with are not the same nationality as me, or that I spent most of my adult life living in an extremely multicultural city, and that I chose to live there because of the diversity. I have never made a rude or hurtful comment to anyone on this site. I have never made any racial slurs, and I strongly advocate sticking up for anyone being beaten down in any way shape or form. I realise at this point you may have forgotten my question so I will ask again, what leads people to stereo type or judge others? Lack of intellect? Hate? Propaganda? Fear?