I have now been taking photographs for over 50 years( ho hum, I know!) and this sort of argument has always been around. Retouching, enlarger image manipulation, multi exposure images, intentional reticulation, polaroid use, all of these and others have been in contention by some. But many have used these tools and methods for the enjoyment and challenges they can give. I am sure your friend is quite sure he knows what he is talking about, and you are not likely to change his views, so f... em! As Michelle A says " does it really matter". Enjoy, mate!