The term secular is used to distinguish non-religious things from religious ones. The thing need not be anti-religious to be secular; in fact, that would be a misleading use of the term. Instead, describing something as secular generally means it is simply unrelated to religion.
For example, the United States government is, under the Constitution, a secular government. That does not mean the government acts against the interests of religion or the religious. On the contrary, it means that the government must remain neutral with respect to religion, to the extent possible. Furthermore, it doesn't mean that religious people cannot populate government positions. Indeed, in the U.S. most office holders are religious. But government officials cannot use their executive, legislative or judicial powers to promote one religion over another, or religion over irreligion.
"Is there any maxim in politics more certain and infallible, than that both the number and authority of priests should be confined within very narrow limits; and that the civil magistrate ought, for ever, to keep his fasces [bound wooden bundle symbolising judicial authority] and axes from such dangerous hands? But if the spirit of popular religion were so salutary to society, a contrary maxim ought to prevail."
Secular vs. atheistic
Being secular is not the same as being atheistic. Both believers and non-believers (with respect to any particular god claim) can participate together in a secular purpose.