I think often the people who are saying 'Never use a sheet' are saying it because -back in the day- sheets were often polyester blends- people hand quilted- and they were a bugger to hand stitch through---We've come a long way Baby! now with more people machine quilting, with cotton sheets being easier to find, and with our (adventurous nature) it is becoming more acceptable....one thing is true though---the quilting cottons you purchase at the quilt shop is *generally* about a 60 thread count fabric---sheets are much *denser*---but if you buy 100% cotton, and prewash it- it softens up- and they really are not so difficult to stitch through- even by hand....if you want to use a sheet- then use a sheet---no one needs to know except you---if you find yourself surrounded by the ^quilt police^ who are preaching the sins of sheets, simply smile and keep your little secret to yourself- they will oooh & ahhh over your quilt without having any idea---and if they ask where you found such a wonderful backing....well...play it by ear- 'just got lucky & found a good deal' or tell them---JCPenney white sale
..often I just tell people- oh I shop on line a lot- who knows where that fabric came from---it's fabulous though isn't it?