Why are ordinary civilians penalized the same way as corporations?

Because corporations are people. As is officially recognized by the U.S. courts

P.S. Sarah, Halliburton as an entity on paper did not cause anything, and it should not have been fined anything at all. The people who were calling the shots and doing those shoddy inspections should be held liable. Ultimately, however, the guilty one in this case is the shareholder.

They aren't. Halliburton admitted to causing the deaths of 12 BP oil rig workers, due to their own shotty inspections. Their penalty was a mere $200,000 fine. If YOU killed 12 people, you would get the death penalty.