because Dagan isn't the only oneamong present and past security experts who believe the same as he does. He's just the most outspoken of those who are ABLE to speak without jeopardizing their position. By the way...even your friend Lieberman has stated that Iran poses no threat to Israel...although recently he's more silent on the issue...lol...but that's cuz Bibi's working on convincing him to support an attack...
Islamic State blows up tower tombs in Syria's Palmyra (Reuters)
from the article: Former Mossad chief briefed comptroller about Iran strike plans