When creating a topic, the guardian check for permission to create is bypassed if
skip_validations is set to true:
However, when creating a reply the equivalent check is not bypassed:
Perhaps I am missing something but this looks inconsistent to me, i.e.
skip_validations should bypass the guardian check either in both cases or in none of them.
In any case, I fixed this because I needed it myself (to have an importer create posts in private categories). Here is what I did: