Two things that I think could be a problem are the following:
1.If a moderator deletes a post because he thinks it’s L”H, and writes “edited because of l”h”, he has now written either Motzei sheim ra or loshon hora about the poster, and there is no reason for it, since the post was deleted anyhow, so it’s unnecessary for everyone to know that the Moderator thinks he wrote something that was l”h. In some cases, it is also rechilus.
2. On the other hand, if the moderator posts a post that he thinks is loshon hora and then labels it as such, that is also loshon hora. If he really thinks it’s loshon hora, then shouldn’t he just delete it and send a private message to the person if he thinks it’s necessary?