In my previous question someone pointed out that unnatural HDR based  toning will get more objections from the  photography community than cropping. I personally feel that slight HDR based enhancements are OK from an artistic perspective as long as the final image is not changed drastically.

My question is why is hardware based manipulations like black and white photography( traditionally using b/w camera) , long exposure etc , which also result in an "unnatural" image, are acceptable while software based manipulation(like HDR) is frowned upon?