With statements like "left handed people can reason too" or "I drove a red car and nothing happened" you are implying a doubt, that the opposite could be an idea worth considering. If a prejudice has a context, that context is relevant - otherwise the idea is presented as general.

[Edited for content a second time: I quoted an article I was just reading by chance, presenting data that are exemplary of another point, about the relation between generic statements and actual differences: I now remove it realizing I missed a detail in that quote that excluded the professional context.]