Flags by default are anonymous. As others have already pointed out, the anonymous nature of flagging a post means that people will dare to speak up without fear of repercussion.
If someone flags a post, they are also given the option to start a conversation with the person they are flagging. So those who want to be known, can make themselves known. We do see this happen, where people not only flag, but add a note about why they flagged a post and what could be improved to get the point across in a non-flag-worthy manner.
Admins and moderators do see who flags who. So if people are abusing the system it is visible, and better still because we don’t just see if someone flags a certain user a lot, but if they flag a lot in general. So far, we have seen nothing that qualifies as abuse of the system.
We have seen posts flagged that we felt did not need to be, and since moderators have multiple options beyond just accepting that a flagged post is bad and needs deletion, we act accordingly.
If anyone feels that a lot of their posts are flagged and do not know why, then I suggest starting with: