Argument: Entry into the Martian atmosphere is very hazardous
"Going to Mars: A mission fraught with risk." Canadian Space Agency. September 9, 2003: "Hazards of entering into the Martian atmosphere. Entry into the Martian atmosphere is a crucial stage of the mission and represents a massive obstacle to its success. Various factors—such as the density of the Martian atmosphere, a sandstorm, an outcrop of rock, the spacecraft's speed, a faulty trajectory, a lack of fuel, or an electronic glitch—could jeopardize a mission. Many missions have, in fact, failed at this stage."