Freedom of religion

Millions of innocent men, women and children, since the introduction of Christianity, have been burnt, tortured, fined, imprisoned: yet we have not advanced one inch towards uniformity. What has been the effect of coercion? To make one half the world fools, and the other half hypocrites. To support roguery and error all over the earth. Freedom of religion is the right to worship (or not worship) in any manner you choose.

As a basic freedom
Freedom of religious worship is included as a specific case of freedom of expression and freedom of speech. In general, what a person believes doesn't actively harm others, yet holding and espousing any number of beliefs may expose that same person to persecution. To address this, freedom of religion is a protected right.

Codification

 * Australia — since the Constitution was drafted in the 1890s, section 116 has prohibited establishing, imposing, or restricting any religious practice, or religious tests for office
 * Brazil — Codified since 1890, in the constitution since 1946
 * Canada — Freedom of religion is a constitutionally-protected "fundamental freedom" according to the Canadian Charter of Rights and Freedoms, subject to "reasonable limits prescribed by law as can be demonstrably justified in a free and democratic society"
 * China — The Constitution of 1982 grants freedom of, and from, religion to all of its citizens. However, in reality, only religious associations which submit to the state can observe their beliefs unmolested.
 * Estonia — Constitutionally-guaranteed in article 40
 * France — In the constitution since 1798, and followed up by the policy of "laïcité" — officially mandating separation of church and state — since 1905
 * Germany — Article 4 of the Basic Law guarantees "freedom of faith and conscience" and the right to practice religion undisturbed
 * India — Guaranteed in article 15 and Article 25 of the Constitution of India, and a preamble amended in 1976 states that India is a secular state
 * Ireland — Article 44 of the constitution ("subject to public order and morality" though) ; until 1972 the Catholic Church was specially privileged
 * Japan — In the constitution (article 20) since 1946
 * Mexico — Since 1859. Clergy cannot run for office, or make political statements
 * Netherlands — In the constitution since 1983, though religious schools receive government funds
 * New Zealand — Codified in the New Zealand Bill of Rights Act 1990, section 15
 * Philippines — Codified in the 1987 constitution
 * Poland — In the constitution
 * Portugal — In the constitution since 1976
 * Spain — In the constitution since 1978
 * Switzerland — In the Swiss Constitution since 1874 ; Article 15 in the 1999 Federal Constitution
 * United Kingdom — Guaranteed since the ratification of the European Convention on Human Rights, strengthened since the passage of the Human Rights Act 1998. However, the UK does have an established state religion ("Cake or death?" ) and the abolition of legal penalties for blasphemy was shockingly recent (2008)
 * United States — Freedom of religion is guaranteed by the Establishment Clause and Free Exercise Clause of the First Amendment of the constitution and is closely associated with separation of church and state (known as the "wall of separation")

Freedom from religion
While there are (apparently many) on the Religious Right that disagree, freedom from religion (e.g., the ability to be an atheist, secular humanist, and so on) is an integral part of freedom of religion. This is because without the ability to choose to not partake in religious activity, the free choice of religious activity becomes meaningless. Freedom of choice requires informed consent, and a cornerstone of this is the ability to withdraw consent — otherwise it's coerced, and therefore not free consent. If the option to not be religious is removed, then being religious becomes effectively forced and the power that the belief has (because it was chosen out of all others, including the "N/A" option) is diminished.

Criticisms
There are multiple problems with the concept of freedom of religion, and how far a person's freedom of worship should be protected:
 * Religion and culture are often deeply intertwined. Many wars are religion-based (or religion is used to justify them ad hoc), many countries have a dominant religion or religions even when there is officially no religion that is endorsed or supported by the state, and worshipping contrary to the state (or, even worse, following a religion that happens to be seen as a threat) is seen as an act of civil, not religious, disobedience. The "9/11 Mosque" brouhaha is an example of this.
 * Religion often demands actions from believers that offend the culture they exist in or conflicts with the values of the land. Examples include:
 * Smoking ganja for Rastafarians
 * Use of psychedelic plants
 * Polygamy for Muslims, Mormons, or anyone else seeking to emulate the many polygamist prophets found in the Old Testament. In 1878, the Supreme Court decided that polygamy was illegal, even for Mormons.
 * Incest for anyone who noticed Sarah was Abraham's half-sister
 * Killing non-believers, believers of other religions, apostates, homosexuals, non-virgins on their wedding nights, and those who work on the Sabbath
 * Chanting up and down Oxford Street for Hare Krishna worshipers
 * Animal sacrifice for various religions, when the animal will be used as food
 * Human sacrifice for Aztec revivalists
 * Declining medical treatment for your children on religious grounds. In 2011, the state of Oregon decided to remove religious conviction as a defense against homicide charges faced by parents who shun medical care for their kids.
 * Monotheistic religion, by its very nature, tends to demand that it is the only true religion. "Thou shall have no other god but me," as Yahweh put it. As such, those religions tend to frown on religious freedom for infidels (i.e. the rest of us).
 * Religion has historically been used as a last resort argument against, well, everything, but notably integration, and freedom of religion used as an argument to support discrimination in public accommodations, services, etc. To this end, the religious right has co-opted the phrases "religious freedom" and "religious liberty" as euphemisms for their bigotry and their desire to continue controlling others.
 * People that belong to a well-codified religion can find it easier to assert certain rights ("I would like to have a cross in my hospital room because it gives me comfort") than those that do not ("I would like to have a funny picture of a pig in my room for the same reason").