I'm not opposed to all stereotyping, just the wrong kind of stereotyping. I think we all know it when we see it: "Jews are all greedy, Poles are all stupid, Mexicans are all lazy." Generally, greed, stupidity, and laziness are frowned upon in our culture. The gaydar thing is only wrong to a person who already thinks there's something wrong with being gay. One might make the argument that it's making fun of gay people for having meticulously kept and preciously decorated houses, but I think most people wouldn't say there's anything really wrong with such decorating--it's just not how they, personally, would choose to decorate their own houses.