I like it. Actually, the only time I ever hear about 'purity' in regards to cropping is from people who crop when they talk about people who don't. I just tend to choose from the infinite number of possible images that I can make full-frame...as opposed to using any of the infinite number of possible images that are created by cropping the image on the film. Those who do both (full-frame/crop) do not have any more choices, because infinite is infinite...there is no more, and no less, infinite...
I am using 5x7, 8x10, and 11x14 cameras, printing the full negative (including its rebate as part of the final image). Cropping would mean that I would be showing a print that is presented significantly differently from the rest...which is fine in some situations, but mostly not when working on portfolios. YMMD
I use modified darkslides to expose two 4x10 images and two 5.5x14 images on 8x10 and 11x14 film respectively...while keeping a rebate around each image...so technically, I am not cropping down from an 8x10 image to get a 4x10 image.