Harriot did not need to explain - everyone understood what he meant even without it. However, explicitly stating the probable outcome, which was straight up death even for a Dao Lord, certainly put the risks in perspective. Of course, the outcome was not certain - it was just what Harriot assumed would happen based on the fact that it would not be easy to handle the karma originating from so many Dao Lords, let alone Eclipse. No one bothered to correct it. It would be moot to do so.
Consenting to be subject to such a karma was a clear indicator of the importance of what was to come. Of course, simply not revealing what happened here, and not harming one another were too specific restrictions, leaving much room for the knowledge gained here to be used in other ways.
For example, if Lex suddenly went crazy and revealed his identity as the Innkeeper, even though no one would be able to spread that news, or harm him because of it, the Midnight Inn would effectively be doomed.
