Scarpa was dangerous because he was a rat. Demeo and his crew shit on Scarpa and company. Compare rackets and body counts. Nobody would go after Demeo and company but the Orena faction had no problem going after Scarpa. If someone tried to kill Demeo while his daughter and grandkid were in the car with him, it would be catastrophic. Yet, the Orena faction had no problem doing that to Scarpa. At the end it took a lot of planning, double crossing, and a trade from another family to take down Demeo. Scarpa died due to ignorance. At the end of the day, it was people who both men trusted that got them killed. Scarpa with the aids tinged blood and Demeo with Gaggi and the twins. One's son went to prison for the sins of his father and the other's died because he couldn't get over the sins of his father.