General Motors on Monday announced that it is eliminating 15 percent of its salaried workforce and halting production at five of its North American auto plants in an effort to save $6 billion by 2020. Investors reacted to the elimination of 14,000 jobs by driving the company’s share price up by nearly 8 percent immediately following the announcement. That combination of unemployed workers and happy investors underscores a key point about the modern American economy: What’s good for corporate profits isn’t necessarily good for workers.