All these shows set a precedence from the very beginning that they are ruthless, and will keep showing you that. 'Game of Thrones' introduces us to three characters in it's opening scene and by the 10 minute mark all three of them are dead. 'Breaking Bad' shows the audience in it's own first episode the horrific result of messing with Walter White by placing Krazy-8 and Emilio in the center of a phosphine gas explosion that only one of them will regret living through. Heck, The Walking Dead begins with the apocalypse and 'Dexter' is about a serial killer.
In fact two of the most memorable scenes from Breaking Bad and Game of Thrones come in the form of brutal massacres. The infamous Red Wedding from Game of Thrones has become a defining example of the show-runners' callous hearts and the Breaking Bad scene where the brilliant and brutal Gustavo Fring mass-murders the Cartel with a poisoned bottle of tequila proves equally memorable. It is the moment when the audience finally sees what the mysterious character's motivations were and the full extent of his capabilities.
Don't be afraid to skimp on the death-count because if anything the audience will only celebrate your show further.