I can see your point oldsoldier, and for casual crime, visual deterrence would seem sufficient. From our perspective, a church is not a very likely casual crime risk, and advertising a security force presence there only allows an intended criminal to make better plans at overcoming the defenses. Were we dealing with something like vandalism or burglary, then a conspicuous camera placement and an alarm system would probably take care of the threat. However, our biggest risk is an armed attack during services (risk being a product of likelihood and magnitude). For this reason, clandestine armed presence seems to be the best mitigation against the greatest risk, and so our security team is independent from the administration as well (as members of the church, we are all stakeholders in the general welfare, and do not need consent from the executive level since there are no provisions against members being in church legally armed otherwise).

Given the situation that unfolded in Colorado Springs a couple years ago, where an armed assailant was neutralized by an unidentified armed security member in a church, this plan of action seems prudent and germaine.