 Why is the rumor that Martians can read minds especially scary to Ben?
Most of the big room lay obscured behind a shimmering veil of tobacco smoke and the sweet, heavy fumes of Martian Devil's Egg. There, among the grizzled veterans of the old Moon Patrol, he'd found friends who understood his dream and who later recommended his appointment to the U. S. Academy for the Conquest of Space. Under interplanetary law, that would mean ten years in prison and a dishonorable discharge. Or— There were old wives' tales of a group of renegade spacemen who operated from the Solar System's frontiers. And whereas no legally recognized ship had ventured past Mars, the souped-up renegade rigs had supposedly hit the asteroids.
 If they can, they definitely know he's guilty of what he's done.
 If they can, they definitely know he's guilty of what he's done.  It would mean that Martians are fully aware of what Earth people are thinking, and manipulating them.  If they can, he's uncomfortable with the notion that they can read his thoughts.  Not being able to confirm if it's true or not makes Ben wary of interacting with any of them.