I personally think that replicas are simply great and that they really help in propagating Art. Now, one has to be practical, if you want to stick to one Painting that a great Artist made, that means only one person can have it. And if you give a chance to only one person to make duplicates, then we don't get a fair deal.
Art, is all about bringing together different classes, it knows no boundaries, and no cash constraints. So, these replicas, gives a great opportunity for many art lovers to get a famous painting. There are many art lovers who cannot afford to go to well known museums and see the paintings, and for them this is a really handy advantage.
What it really does is that it promotes the work of the Artist even more and results in the Artist being famous and some emerging Artist getting money to live. So it actually brings a lot of positive points to all spheres.
If there are more artists who are into replicating the works of famous Artists, that means a lot of emerging artists gets a means to survive and also like I said in the beginning it gives us a wider choice and better price.
The only negative points that I can see is that, all budding Artists might want to get into creating replicas and there can be a dearth of new concepts and paintings. The other thing is, there are chances that some artists can make a complete disaster out of the masterpiece and sell it to unsuspecting people. There can be a big variance in quality, and that can result in the original looking bad.
It would be really not right to think that all the big Artists will not be happy that their piece of work is being copied and replicated. They would really love it.