It doesn't "speak volumes about how single people are viewed in our culture." It's just a quirk of Prudie's. One data point.

Also, no one has stated or implied that they approve of bringing a non-invited guest. Rather, the question was, who should be invited?

Meanwhile, your use of the term "singlist" speaks volumes about the chip on your shoulder. Sorry, but I don't really see a need for "progress" here. People know how to be polite (sort of, mostly) and don't need to have their consciousness raised against "singlism."