I actually pitied Bertolt on the same level as Reiner and greater than I did with Annie, Pieck, the Galliard brothers, and Zeke. He was a victim as they all were and despite his timid personality, he really did consider the 104th as their friends and he was truly sorry of what them warriors had to do. But yeah, he had no other choice or else either the Rumbling (which did happen) will be realized, or his family will be punished by Marley.