[eeyore]

I agree with you up to a point on the predators thing but there are other considerations such as:
what happens to the bird if the tamer movers away as presumably they will have become its prime source of food,
what happens if it meets some less well intentioned people who might think it funny to do it harm
Will the taming also have altered its behaviour so much that it finds it dificult to interact with other robins, get a mate etc.
And finally do we have the ethical right to interfere in nature in this way ?

Personally I wouldnt unless it was absolutely necessary to save the creatures life.