From what I've read on the subject, it used to be considered a disorder, but no longer is considered one. If a person actually wants to practice this, they can find partners who are willing to be the consensual recipient of this practice. As long as its consensual with boundaries that are respected then its fine IMO. If a person is inflicting it against a persons wishes then obviously that wouldn't be good. People who partner up, usually have safe words and negotiate what they will and won't do beforehand.