Some people are angry that there is a tank in Brotherhood due to it being historically inaccurate. Well the tank and the flying machine were both designs of Leonardo Da Vinci, but they never came to life. And if people don't like the tank because of history then why did people enjoy a "flying demon" soaring across Venice to the Palazzo Ducale? If everything in Assassin's Creed was true to history then the game would not be at all fun. And there will still be stealth.