In the sphere of traditional Irish instrumental music there's still quite a fierce emphasis on learning tunes by ear being the only right way to learn 'em. I've learned a lot that way but I can't deny that I've learned a good few from CDs. To me that's second-best but I wouldn't say it's unacceptable - as long as you've learned plenty the hard way, which generally means going to play in sessions. At least if you've done that you've learned not to be inflexible...