Human rights treaties commit nations to freedom of religion or belief (including freedom of nonbelief and nonreligious beliefs). Any constraints on freedom of religion or belief should be the minimum compatible with the survival of a liberal, tolerant, democratic open society. In addition the European convention on human rights includes a commitment to the principle of nondiscrimination.
From this it appears to follow necessarily that the state, the law and the public institutions we all share must be neutral towards different religions and beliefs. On questions of profound disagreement and deep sensitivity where there is no agreed way to establish the truth or falsehood of the claims made variously by Christians, Muslims, humanists and everyone else, it is quite wrong for the state to throw its weight behind any one particular religion or belief. This neutrality is what is meant by secularism. It is a political principle applicable to states: a secular state may be supported by religious believers and be the home of widespread religious belief. Indeed, secularism is the best guarantee of freedom of religion or belief – but the enemy of religious privilege. It must be distinguished from a secular society, a term that suggests a society that has distanced itself from religion.
Now there is a common riposte to this: that neutrality is impossible, that a secular state in fact imposes liberal, secular values on everyone. In the Italian crucifix case, partisan law professors went so far as to claim: "An empty wall in an Italian classroom is no more neutral – indeed, it is far less so – than is a wall with a crucifix upon it." But this is playing with words. Laws, government and institutions that do not impose or assume any religion or belief on the part of any individual citizen leave the individual free to hold any religion or belief, or none. Is it dictatorial to remove chains from contented prisoners? They need not leave their cells if they prefer to stay. By contrast, those who reject secularism seek to fit everyone with their own style of shackles. This is not an enhancement of the freedom of the dominant religious group but a curtailment of that of all the minorities. By contrast, secularism is the best possible guarantor of freedom of religion or belief for everyone.
Objectors often allege that humanists and other secularists wish to drive the religious from the public square. Not so. How could we, when atheism or humanism are in law no less "religions or beliefs" than Islam or Christianity? If Christians were banned from the public square, so would be humanists and atheists. (Moreover, the phrase "the public square" needs further analysis: there are different types of public space for which different conventions are appropriate.)
http://www.guardian.co.uk/commentisfree/belief/2011/jul/07/secularism-neutrality-religion-atheism