Would it be possible to use a list of keywords that site writers are restricted from using? So, for example, if the build process sees any instances of these bad keywords in a list it automatically fails the build. Could be great for managing negative comments and other user generated content. Does Hugo support anything like this?
You’re really dealing with two different things here:
For static content on your site, you could go with the solution by @alexandros
For comments, it would depend on how you have it implemented on your site. It would most likely have to be handled through whatever comment system you’re using
This can be done outside of Hugo. If you use a CI provider such as CircleCI, Travis CI, or GitLab CI, you can write a script to check for those words in your Markdown and fail if it finds them.