question:  Why does Macklin have objections to going back?
context: But Macklin is exactly what we need for a quick, dramatic test. "When we prove our results that should be of enough practical value for anyone. "But now Macklin—" Elliot Macklin had inherited the reputation of the late Albert Einstein in the popular mind. No one knew whether his Theory of Spatium was correct or not because no one had yet been able to frame an argument with it. The government took up a lot of his time using him as the symbol of the Ideal Scientist to help recruit Science and Engineering Cadets. For the past seven years Macklin—who was the Advanced Studies Department of Firestone University—had been involved in devising a faster-than-light drive to help the Army reach Pluto and eventually the nearer stars. Macklin threw a big arm across Ferris' shoulders. "No, Harold, it isn't," Macklin admitted. "I would have said the common cold," Macklin replied, "but I suppose from what you have said you mean headaches." "Aspirins would still be used to reduce fever and relieve muscular pains," Mitchell said. "There are a number of different causes for headaches—nervous strain, fatigue, physical diseases from kidney complaints to tumors, over-indulgence—but there is one effect of all of this, the one real cause of headaches," Mitchell announced. A colony of virus in the brain cells will relax the cerebral vessels—and only the cerebral vessels—so that the cerebrospinal fluid doesn't create pressure in the cavities of the brain." Conscientious objectors from the Army." "We want you," Ferris told him. Unless we can produce quick, conclusive and dramatic proof of our studies we can get no more financial backing. "I'm tempted," Macklin said hesitantly, "but the answer is go. "When your heart stops, your blood pressure goes to its lowest point," Mitchell said. A dew of perspiration had bloomed on Macklin's forehead. Ferris and I are confident that there is no danger....
output:  He doesn't want to go back. He'd rather be "stupid" than having headaches and always worrying.
options:  He doesn't want to have to undergo another experiment.  He doesn't want to go back. He'd rather be "stupid" than having headaches and always worrying.  It's too risky to try the experiment again. He'd rather take his chances the way he is now.  He doesn't want to go back. In the state he's in, he's too "stupid" to realize the ramifications of what happened to him.