Secularism is the State being neutral on religion so that one religion is not
privileged over another or none. It is certainly not the same as atheism. Indeed
many people who are religious are also secularists because they want everyone to be
free to believe what they want and to choose the religion they want.
Now, many religionists don't want that: they want to force people to be, say,
Catholics. However, it is far better for someone to want to become a Catholic than
to be coerced into it, perhaps by subtle messages that that is the one religion
supported by the State.