It would be best if you could get a variety of fats if possible, but in a pinch, or for temporary periods butter is a great fat if you have to choose just one, so long as you're able to digest it.
Like DF said it's obviously not natural to be getting all your fat from dairy, that doesn't automatically make it bad, just keep an eye on it if that's what you're going to do and if you run in to trouble, keep that in mind as a cause.