pros and cons I see coming to lite:
If you wash, you must starch, but bugs love starch...
Unwashed gives a nice crinkled effect after washing the finished quilt
Washed then starched gives a wonderful 'flat' finish to your work
Unwashed can run colors, but so can washed
Unwashed you must handle with care in the steam from the iron as it will shrink unevenly, so a dry iron must be used.
Formaldehyde is a nasty chemical!! No getting around that one.
Starch can cause discolorations and make creases and wrinkles permanent.
I guess it comes down to this. Treat your fabric as it would be treated in the end. In my case, I make quilts to be used, hens, washed again and again. I like the crinkled look, so I don't wash before but wash the hello out of it before it is used.