From a grammatical point of view, there is nothing wrong with the passive, of course. And there are many instances in which the passive is the best choice. But in other instances it is frowned upon as it can lead to an amorphous and obfuscating language in which nobody is ever clearly responsible for anything.
or, putting it in a more active way:
The passive is useful, in its proper place, but several proponents of a clear style (such as George Orwell) advise against overindulging in it, as it can lead to a style better suited to hide information than to reveal it.
The difference, in short, between
"the buck stops here"
"errors were made"
I wrote the above to answer someone on another forum; he was asking why MS Word’s grammar checker always flagged the passive voice.
As with so many other “writing rules”, the suggestion not to use the passive voice when the active one would do should be taken with a pinch of salt. I use the passive when necessary, of course, but I also find that trying to change passives into actives helps me tighten up my writing.