I'm talking about all religions and every religion in general. What are your reasons?
Religion and religious persons impose their faith into public policy and politics. Where it clearly doesn't belong.
Religion is still very much mediatory in the schools of nations such as Republic of Ireland, where it has no place. Churches were built for a reason. This makes many members of other faiths and no faiths feel uncomfortable and excluded during a time when young persons find it difficult to fit in as it is. It isn't a matter of talking about religion, but actively telling young persons to practice it mandatory.
Many nations make it difficult for the non-religous to have any sort of successful career in politics (and being honest about their lack of faith at the same time)
Many religious groups impose their views of abortion on others and seek to make abortion illegal. Because of religion in other nations it now is or has been for sometime, outlawed medial practice. Abortion is not murder, murder is the illegal killing of a human being, not a pre-human being.
Religion demonises many educational fields in contrast with its doctrine, such as certain aspects of history and many accepted theories
There have been cases in the United States and some other country where person's have lost their jobs due to lack of faith or alternative faiths and sometimes on the bases of sexual orientation (which is thought to be justified because of certain beliefs)
Religion tries to justify many forms of discrimination including but not limited to, homophobia, sexism, racism and class
Certain nations such as Iran and Uganda take their discrimination justified by religious beliefs a step further by improving atheists and murdering homosexuals
Religion has caused many to rebel against its corruption. While this mostly occurs in changing religions or declaring oneself atheist; that is not always the next direction for some. For some they take that faith and change it for their own purposes, often resulting in more extreme and harmful faith systems mostly regarded as cults. These cults involve all sorts of dangerous acts, such as mass suicide and sometimes violent attacks of non-beleivers of their faith.
Religion has literally caused people to go to war due to the influence of the faith and disagreement with certain policies based on religious beliefs (especially when a doctrine influences such actions)