Au Contraire!
They advertise "cotton is the fabric of your life" because it feels so nice against your skin. The 10% Lycra content in the Capezio dance belt just gives it some stretch without losing the cotton texture and feel. It is certainly thick enough to do its job.
I can't argue whether they are "evil" or not, but I do think dance belts have an unjustified bad reputation for discomfort. Once you get used to the strange sensation of having a tight thong riding in your crack, they really aren't that bad. And the support they give is unequaled! Like you say, they are necessary. [/i]