How can people say insurance companies should be able to deny based on pre-existing conditions?

Let's look at an example. Bob has a job. He has health insurance. He gets cancer, and his insurance company pays for his tens of thousands of dollars worth of treatments. The economy goes south, Bob gets laid off. He has to choose between health insurance and losing his house, so he obviously needs to stop the insurance. Later, Bob gets re-hired, and despite the fact that he can afford insurance, he can never get it again, because he has a pre-existing condition. But no, we need LESS government regulation of the insurance industry. LOL!