@Rayodino
Until he builds up fame, connections and power in the world it won't be a good move to inform the other guilds when he can't provide the source for the information and they won't believe him even if he did as he is considered a newbie hunter still.
Also, it will bring up questions of how he knows and if he is connected to all this. With him being stuck in tower for so long, it gives plenty of grounds for such suspicions.
Plus it will clue in people trying to erase him that he is a far greater threat than they had estimated thus increasing the danger to MC and his friends.
So wouldn't call it stupid but it is morally lacking to knowingly put people's lives in danger. But hey he never purported himself to be a hero or saint.