 Why was Peter Karson initially relieved when he first heard the news of the invasion?
He had been dead for some time now, but the dark blood was still oozing from the crushed ruin of his face, trickling down into his sodden sleeve, and falling, drop by slow drop, from his fingertips. Outside, the stars were as before: tiny, myriad points of light, infinitely far away. It was a kind of indefinable emptiness. I do not think it was what Peter called an emotion; and yet it had nothing to do with logic, either. Young Peter Karson put the last black-print down and sighed with satisfaction. His dream was perfect; the Citadel was complete, every minutest detail provided for—on paper. Then there would remain only the task of blasting the great, shining ship out into the carefully-calculated orbit that would be its home. He could see, too, the level on level of laboratories and storerooms that filled its interlocking segments; the meteor deflectors, the air renewal system, the mighty engines at the stern—all the children of his brain. Out there, away from the muffling, distorting, damnable blanket of atmosphere, away from Earth's inexorable gravitational pull, would be a laboratory such as man had never seen. The ship would be filled with the sounds of busy men and women, wresting secrets from the reluctant ether. He stared at them dully, and then he reached over to the newsbox on his desk, and switched it on. The order was made public early this morning by R. Stein, Secretary of the Council, who said in part: "The reason for this ... order must be apparent to all civilized peoples. There can be few within reach of printed reports or my words who have not seen the Invaders, or whose friends have not seen them. "The peoples of the world, then, know what they are, and know that we face the most momentous struggle in our history. "Since the Invaders first appeared in Wood River, Oregon, 24 hours ago, they have not once acknowledged our attempts to communicate, or in any way taken notice of our existence as reasoning beings. They have treated us precisely as we, in less enlightened days, might have treated a newly-discovered race of lower animals. They have examined us, dissected us, driven us mad, killed us with no discernable provocation; and this is more intolerable than any normal invasion. "I have no fear that the people of Earth will fail to meet this challenge, for there is no alternative. Not only our individual lives are threatened, but our existence as a race.
 It confirmed that what he saw was real, and he wasn't losing his mind.
 He was glad to know he wasn't the only person who had seen something.  He was glad to hear it reported, rather than ignored.  It confirmed that what he saw was real, and he wasn't losing his mind.  He feared he was going mad and was relieved to hear something from the real world.