My stance isn't that they shouldn't have been done, but that they were done poorly. This really didn't start being an issue until film number 5. Up til that point the films had managed to remain faithful yet interesting adaptations to the books.
Then number 5 happened. Almost eveyone I talk to about the fifth book says that it felt rushed, and it did. There was way too much ground to cover in the amount of time the films take. The problem is the way they chose to work around that. Certain characters were nerfed (Ginny), subplots were summed up in single dialogues, and, in general, the film felt like the director was trying to do as much as possible in as little time as possible.
The sixth film was actually better, partially because it chose to mix things up a bit. A lot of fans were upset that many of the things in the movie never happened in the book (the beginning flirt between Harry and the waitress for e.g.). However, with some exceptions, I felt that these elements improved the movie, because they provided a way to get the information about the characters and story across without having to do the rush job the 5th one did.
Still there were two things I REALLY hated. One was an action sequence in the middle of the film that seems to have been put there for no other reason than to have an action sequence. Though, it did slightly help the other thing I didn't like.
The second is Ginny. This goes back to the 5th movie again, because the fifth book was when she finally got over her Harry-phobia and start expressing her personality (which is pretty much what you'd expect from a girl growing up with 6 brothers). The film, however, shoves her development to the side. Then in the sixth movie, Harry suddenly falls for her. Even though she still is practically without a personality. In the books, the characters have great chemistry because of Ginny's personality (strong, willful, and funny), but in the movies she never moves past the mousy character. And it's hard to imagine Harry falling for that.
I haven't seen the latest movie yet, but I'm hoping that since it's part 1 of 2, that it will finally give the series the chance it needs to explain sh** and set the sort of tone the books had.