Films are not works of one single man. Actors are artists just as directors and their art is in their performance. Same goes for DPs, special effects people etc. It's like building a church. There's an architect who designs it, but then there's a guy who will do paintings inside, sculptor who will do sculptures for the altar and so on. The work of many people will come together to create that work of art.
Even if you don't agree with that I would like to point that ESB and RotJ were not directed by Lucas, so he was fiddling with other people's work. So using the Mona Lisa analogy, it's as if someone else than Da Vinci came in and said: "I don't like this painting, so I'm gonna repaint it".
And in the end Lucas is not the same man who did SW back in 1977. He's 30 years older, he doesn't have the same youthful bravura that made him write Han Solo as a guy who shoots first. Now he's an old man who thinks it made the character look like a cold-blooded killer. He forgot that was not the point of the scene.
I agree that in 1977 special effects were not what they are today, so I'm ok with making cosmetic changes (I know it makes me sound hypocritical). We can assume that yes, that's what he wanted back then, but he didn't have the technology and money to do it. But changing scenes pivotal to character development or replacing actors with the ones from the new trilogy is just plain wrong.
In the end, like I said before, he should just release all the versions on blu-ray "Blade Runner" style and just let people enjoy them the way they want to, not impose his chosen one on them (I thought he supported democracy not dictatorship).
