Fabric is similar to any other washable product on the market. I would never wear new clothing, bedding etc. without prewashing to get out the chemicals, excess dyes and "junk" that are in them. Especially since as was stated by others, most of these products come from overseas and are not monitored. Who knows what's in them or on them! I would never throw new sheets, out of the package, on a bed and I would not do that with unwashed fabric in a quilt, either.
Are you expecting manufacturers to prewash fabric and keep all chemicals out of it? Then you need to only buy organic material and even then I would prewash for shrinkage.