The answer to this question can vary depending on the specific laws and regulations in the jurisdiction where the situation takes place. Additionally, cultural norms, social expectations, and individual beliefs may influence the outcome.
From a legal perspective, in some countries or states, businesses or service providers may be subject to anti-discrimination laws that protect individuals from discrimination based on their religious beliefs (or lack thereof). These laws may prohibit a service provider from refusing a customer based on their religious affiliation, including baking a cake with a religious theme.
On the other hand, some countries may uphold the principle of freedom of religion and expression, allowing individuals to refuse to participate in activities that go against their deeply held beliefs. This means that an atheist baker might have the right to decline baking a cake with a religious theme if it conflicts with their convictions.
It's important to note that while laws and legal principles provide some guidance, the real-world application can be more complex and subjective. If a situation like this arises, it is best for the parties involved to engage in open and respectful communication to find a resolution that respects everyone's rights and beliefs. In some cases, finding a compromise or referring the customer to another baker willing to fulfill their request might be a suitable solution.