Generally an employer *can* dismiss an at will employee simply because he or she doesn't like that employee. It's not *fair*, but it's not unlawful.
Under general principles of law, where employment is held at will, an employer may terminate an employee for any reason except unlawful discrimination (race, gender, national origin, religion, etc.), unlawful retaliation (such as for cooperating with an investigation into sexual harassment), or for reasons that violate public policy.
Don't take what I say here as legal advice as I'm not licensed to practice law in South Carolina. If you need legal advice, please consult a lawyer who holds South Carolina licensure.