When you have a disability, you might still be able to work to earn a living. You have specific protections for this under the Americans with Disabilities Act and other laws. Knowing these rights can help you ensure that your employer is remaining in compliance with them, which can provide you with an equal chance to support yourself as any fully abled body person would.
No employee should ever have to deal with employment-related decisions being made on personal factors that don't play a part in the business. Title VII of the Civil Rights Act of 1964, as well as some other laws like the Americans with Disabilities Act (ADA), set some clear legal standards for employees regarding discrimination.
Employment anti-discrimination laws are written to protect workers, but they can also be valuable to employers as well. Businesses function more productively when everyone (employees and management) understands the rules and expectations around hiring, firing and management of workers.