Stick your tongue in your cheek, speak, your words are garbled - don't be surprised or blame others when you are misunderstood.
Oh! I see. My words are garbled. Perhaps I made a grammatical error. Let's check. So I did. Surprise! Surprise. I wrote painter's when I should have written painters. Now, with that in mind, are my statements clearer? No?
Okay! I'll take the trouble to explain and amplify the principles. Since I'm not sure which aspects of my statement you're having trouble with, I'll try to be precise and specific, addressing each point.
(1) Cheating is a great human skill.
This appears to be a biological fact. One may quibble about the use of the word 'cheating'. Deception might be more appropriate. Whichever synonym you choose, this skill of cheating, deception, or telling lies, whether big fat lies or little white lies, is a talent in which Homo Sapiens excels. It's a consequence of our big brains.
(2) The scientific method of controlled observation and repeated testing to verify the truthfulness of any theory or hypothesis, is our saviour from the mayhem that results from uncontrolled cheating.
(3) Painters have engaged in deception for thousands of years.
This is undoubtedly true. Artists, whether painters or music composers, have traditionally lived the role of servants to the ruling class, doing their best to please.
If one is commissioned to do a portrait of a wealthy and powerful aristocrat who is possibly, probably, and very likely, a bastard, a hypocrite and a cruel, unthinking and rather stupid man, then one's carreer would end if one were to portray him as such.
(4) Is there some law that decrees photography should be an exception?
There appears to be no such law that I'm aware of. However, we should not dismiss the tremendous effect that the camera has had on painting. It had a significant effect even before photography was invented. I'm using a date of 1826 for the first, permanent photographic image that was created.
Long before that, we had a device or phenomenon called the Camera Obscura, the principles of which go back to Ancient Greece (Aristotle), and the Chinese about the same time, around 400BC.
The camera obscura is basically a pinhole camera without any photographic plate. The image is presented upside-down, and the size of the image depends on the size of the camera obscura, which can be as big as a room.
Unfortunately, the sharpness of the image depended on the smallness of the hole, which also affected the brightness of the image when displayed on a wall or canvas or whatever.
The invention of the lens occurred well before the time of Galileo, and was later instrumental in improving the the effectiveness of the camera obscura for painting purposes.
No longer was one limited by very fuzzy images from a large hole, or very dim images from a small hole. One could get a reasonably sharp and bright image with a good lens installed in the camera obscura.
Not only that, with the use of mirrors one could inveret the upside-down projection and get an ideal image on one's canvas, as a painting guide.
Do you think that Renaissance panters would not have grabbed this opportunity to create a never-before-seen realism in painting? You bet your arse they did!
For centuries before the first photographic plate that could permanenty record the image was invented, art in general had assumed an obvious degree of photorealism.
That's not to say that every painter used the projections of the camera obscura; of course not. A style was set and other painters imitated it, to the best of their ability.
When the 'real' camera was invented, in the early 19th century, the first people to take up the new technology were painters, or would-be painters. Manipulation by whatever means was part of the course.
Nothing much has changed.