Feedback is good. Even when its critical, hard to hear, ill-informed, or just wrong.
But feedback is bad when its anonymous because feedback – no matter how critical it may be – is relational. Its my opinion about you, but “voiced”. I’m not keeping it to myself, (and I’m not telling others ‘cause that’s “gossip”) but instead I’m making my opinion known to you.
But what happens when I tell you my opinion, but I don’t tell you it came from me?
All of a sudden you know what “someone” thinks, but you don’t know who that “someone” is. You could be speaking to them now, or tomorrow, or never even speak to them again. It could even be your best friend. You can’t know.
You can see how giving you feedback, without letting you know who I am, is ultimately very unloving, selfish and cowardly. Its a way of telling you what I think, without any consequences to myself.
So, if you get anonymous feedback, the only way to stop the effects of the selfishness that started it, is to just not read it.
If there’s no name on it, stop reading and throw it.