I think that, in general, it makes sense for public figures to not comment to fans but, in a case of something severe (such as obsessive Fanyu hate toward Med, Yunabot hate toward Adelina, etc.), then it would make a world of positive difference to have a word from the celebrity.
I've seen it happen with well-known figures. All it takes is a couple minutes out of their schedule to write a sentence or two, saying "please don't do this."
To be honest, I'm not a Yuna fan for this reason. I always respected her as a competitor, but she never once said a word against the Adelina hate from her fans (including despicable death threats which continue to this day). It makes it seem that she condones the behavior. (Her leadership with ATS, along with their unfounded accusations against Mariah Bell, does not help.)