I believe stereotyping is always negative, whether it's meant that way or not, because it is impossible to paint a whole group of people with one brush. If the audience cannot tell a character is black without giving them huge pink lips, or gay without giving them a "feminine" speech pattern, then the artists and writers have failed at character creation. It is much better to create a character, especially if you are not of that group, by building who they are and their purpose to the story up first and then assigning them to groups of people. I do believe, however, it is perfectly fine to paint Nazis and the KKK and other groups who exist solely out of hatred with the same brush, as they don't deserve to be shown as people outside of their affiliations unless it's to make a point about how anyone could secretly be a scumbag.

Stereotypical representations have definitely affected me, especially when I was a kid. The biggest one that comes to mind is how little girls are presented, especially in toy commercials. Pink and sparkly princess toys felt constantly shoved down my throat, and things I was actually interested in, like catching bugs and playing with plastic dinosaurs, were "for boys." I think a lot of girls can relate to having an intense hatred for all things pink as children out of sheer rebellion for it being so heavily associated with us. I've definitely noticed, as I have younger sisters, that commercials targeting kids have changed to be more gender neutral, but there is still no lack of sparkly pink toys being targeted solely at girls.