I'm always amazed when I see the myth about not using polyester thread perpetuated. There is absolutely NO reason to not use poly, in fact many of the best award winning machine quilters out there today are using poly like Karen McTavish and Rhonda Beyer. The old wives tale about polyester "cutting" into the cotton fibers in the quilt is a myth
http://www.superiorthreads.com/educa...-and-what-isnt
Rayon, I can see trying not to use. But I too have been guilty of using it when it was the perfect color for a quilt. Here is a link to Superior threads explaining the two main reasons to avoid it in quilting. It is weak and not colorfast when bleach is used
http://www.superiorthreads.com/educa...-fiber-viscose
I don't consider this acts of quilt police. Use whatever you want. Just be aware of the problems that could arise.