It really is simple. No one plans to become ill or injured.
If a person becomes ill or injured and needs medical care that he/she cannot afford to pay for, should that person should receive that care?
Unfortunately, many people without insurance become ill or injured, and they show up in emergency rooms and doctor's offices expecting medical care, and they receive it. Who pays for their care? Everyone else, those people who have insurance. This is not fair or morally right. It is simply wrong.
So, since no one can predict when he/she will become ill or injured and need medical care that cannot be afforded, everyone should have insurance coverage, so they do not force others to pay for their care if the unexpected happens.
Some people may not like paying for insurance, but if they become ill or injured, they will be glad they have insurance. And they won't feel guilty for freeloading on others to pay for their care without paying for the care of others as well. This is because of how insurance works: premiums paid pay for the care of the sick and injured.
For comparison, people may not like paying for private mortgage insurance, but if they want a mortgage, then they pay for PMI until they own enough equity on the property. It is not an option.
People may not like paying for car insurance, but if they want to drive a car legally, they must buy at least minimal insurance coverage. It is not an option.
People may not like paying for health insurance, but if they expect to receive medical care they cannot afford, they should have insurance.
Businesses may not like paying for insurance for their employees. But there is nothing that says the employer must pay 100% of the premiums for that insurance. Many, if not most, organizations divide the cost of health insurance, with the company paying for part of it, and employees paying for part of it.