Rav Yitzchak Berkovits (also spelled as Berkowitz, an expert in the laws of loshon hara) understands that if one follows all the requirements of toeles, there is no prohibition at all. It's not that it's loshon hara that's allowed. Seemingly this would mean it's hutra (but see the end).
I heard this from him in a class on Loshon Hara L'Toeles (8 minutes in). I'm sorry but I can't find it online for free anymore (I downloaded it 5+ years ago). I did find it here for purchase.
The way he explains it is as follows: The way he understands the Chofetz Chaim, the source for the laws of loshon hara, is that the prohibition of loshon hara is defined as lowly speech. Meaning, it goes against human dignity to speak badly about another person. As such, if the person is saying something solely for a positive purpose, and follows all the conditions to ensure that is is for a positive purpose, what can be lowly about it? There's no prohibition at all.
He justifies this understanding from the fact that we don't have a heter/"permit" of toeles for any other prohibition. I can't eat pork for good intentions. I can't embarrass another with good intentions. The difference is then that speaking "negatively" about another for a positive purpose isn't lowly speech. As such, there is no prohibition.
He has detailed source sheets on the topic of toeles. A quick glance resulted in only one source that he used to corroborate this explanation (sheet one, source one). When the Sefer HaChinuch § 236 brings the prohibition of rechilus (which includes loshon hara), he defines the prohibition as follows:
שאם נשמע אדם מדבר רע בחברו, שלא נלך אליו ונספר לו פלוני מדבר כך וכך, אלא אם כן תהיה כונתנו לסלק הנזקין ולהשבית ריב.
[The prohibition is] that if a person hears something bad about his friend, he shouldn't go and tell his friend that someone is saying such and such about them. Unless his intent is to remove damage and to end a quarrel.
We see in the definition of the prohibition itself that it doesn't include positive intentions.
However, an important caveat is defining letoeles. The requirements of the Chofetz Chaim to define something as letoeles makes your chosen nafka mina/practical difference not relevant. It's actually the case that if you say something "extra" or unnecessary, that wouldn't be called letoeles. The Chofetz Chaim also says if you have an alternative, you can't say the loshon hara, as again it wouldn't be letoeles. So it's going to be hard to find a real nafka mina for how to define it.