Biggest (and only) letdown in Witcher 3 image - freedomer

Until today I still can't understand why Dijkstra had to make such a dumb and uncalculated move at the end of the Reason of State quest. In the books and up to that point in the game he is portrayed as a very intelligent man and still he proceeds to trust in Geralt minding his own business in this quest although he knows the past he had with Roche, Ves and Thaler. In my opinion this is the only notable downside in Witcher 3, there should have been an option in which neither Dijkstra or the other 3 would die.