It depends on the purpose of your forum, if it’s a brand or support forum for example… your goal might be to just get people an answer as fast as possible. If the content is incorporated into AI training that could be beneficial. Hopefully if it’s truly an unsolved issue people will still make their way to your site to ask about it, but this is still challenging if they’re going to AI first.
In a more social context AI scrapers are almost entirely useless, because you want people on your community interacting with each other. That might be a good case to try and block them completely.