Constitutional issue: religion
The first amendment to the Constitution says, in full: "Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances."
There are two parts here that have to do with religion. The first part says there can be no religious establishment. That means that if inmates are allowed to hold Jewish or Episcopalian services, for example (which they are), they should be allowed to hold services of any religion, not just "established" religions. That led one prison administrator to ask whether religious inmates were being given rights that inmates without religion did not have.
Yes, they are, and the Constitution supports those special rights. I said the first amendment has two parts that concern religion, and the second part protects the "free exercise" of religion. The Constitution does not protect the free exercise of, say, sports, or science. It does protect, as we see above, the free exercise of religion, as well as speech, the press, assembly, and petition. Any such activities that are so protected by the Consitution have special rights.
I suppose that means that in order to afford all citizens the equal protection of the laws (as prescribed in the fourteenth amendment), we have to define atheism as a religion. There is no such thing as an irreligious person. After all, atheism is a faith. Religious people have faith in the teachings of their religion. An atheist has faith in his own belief that they are all mistaken. So it's not such a stretch, after all.