The assertion that religion is a means of control is not a new argument, but it is one that is particularly appealing to a postmodern culture suspicious of any institution and insistent on the self as the final - and more often sole - arbiter of truth.  In attempting to address this statement of faith - that religions are man-made means for gaining control of others - we have to distinguish multiple lines of possible argument, and decide on the best direction to proceed.

I think the most important initial issue to identify is whether this argument is being applied only to Christianity, or to all religion in general?  Does the person have a beef with Christianity or Judaism (or, to a lesser degree, Islam or Mormonism or other Christina heresies), or do they not make any distinction between the Western monotheistic religions and any assertion of a god of divine source for reality?  

If they want to keep the argument at the generic level, the argument easily could end there.  They are making an assertion of faith - without any more basis for it's truthfulness than any specific religion's claims.  Frankly, they have quite a bit less basis, since religions generally make an assertion about their origins, and not only are these being uniformly ignored, the person is making a blanket statement of faith with no known historical or cultural basis.  No basis beyond this is what I want to be true, or this has to be true because I cannot accept that something else could be true.  However, I think it's a mistake to allow the argument to end there.

First off, this argument allows a person to completely ignore the specific claims and assertions of any religious system.  While that's convenient for them, it's dangerous from a logical perspective.  It doesn't make sense to me that one would completely ignore what an explanation of the universe says about reality, and instead make the unsupported assumption that it must simply be a concoction of some prehistoric group of folks bent on a convenient way of gaining control or benefit.   

Secondly, even if a religious system appears to be used as a mechanism for control (and I would argue that adherents of pretty much every religious system do or have done this at one point or another), this does not mean that this is how the religious system began.  It is an evaluation of some aspect of the religion at this point in time, and extrapolating and generalizing backwards from that.  I think we would all agree that forms of political systems are a mechanism for controlling the behavior of a larger group of people, based on the behavioral norms of a particular group of people.  However, this does not mean that any political system is inherently evil, or without good basis.  We acknowledge that there is truth and usefulness in a political system that we *know* evolved by human reason, so why would someone dismiss out of hand the possibility of truth in a religious system, simply because there appears to be an element of control?  

Thirdly, we need to be careful to define what is meant by control or power.  Does this equate to material gain?  Influence?  Governing power?  Sex?  All of these are possibilities, but we need to examine which ones we're assuming.  For instance, if the argument is made that religion was developed as a means of control of a population to secure sexual advantages and favors to those in control, we would expect to find in religious systems some form of argument permitting those in control to exercise greater liberty or advantage in choosing a partner.  Yet what we find almost universally is the opposite - those in control are often expected to exercise greater restraint - or to give up all together - their sexual behavior.  Similar arguments could be made for the other examples of power or control.  This doesn't mean that there are exceptions that act outside of the expected parameters, but if a system was designed by people for control, it seems far more likely that there would be provisions for the special status of these leaders.  This is the case with political systems.  Abuses of political power are frequently along the lines of exploiting or overextending perks and privileges already granted to those in power by the system itself.  

I understand the distaste of abuse of authority.  But the argument that authority in and of itself is evidence of insincerity or non-truth doesn't seem to be a logical outcome or conclusion.  

Other thoughts or ideas on this?  I'll probably be posting more thoughts on this as well.  And hopefully, if my friend is lurking, she'll know she's invited to join in with her own comments and clarifications!