All of them have merit. Priorities must be set clear on what is most desirable; mitigating (or outright extinguishing) the utmost undesirable of behaviors, fostering others, through any means those in power wish to do at their Will; to come about the conclusion as to how they, and you, see this community.
This is an answer, I feel, that leans toward structured, groomed content.
Depends on the community in any given context, if that is more valued. Deleting content for the sake of keeping the presentation orderly can swiftly veer into–
–that kind of territory. This I have seen. The most pathological form comes from crowd/social psychology as the spiral of silence.
I only offer this viewpoint for future readers to consider the “collective consciousness” of their community overall, while also attempting some form of order to the topics themselves.
The default FAQ has a good start to this. Duplicate content is not specified (“Keep It Tidy”). Flags can be used too.
Lots of options to consider from tools already in place.
Then again, I do not know the specific context here for the community mentioned; the social mentality expected, upheld by the staff and/or the users themselves.
Lots of variables, I see.