Tactful skeptics can do a great service to believers. The questions and arguments they present to believers, can help believers to modify some of their beliefs, so that their paradigm is less discordant with reality. It hopefully can help eliminate alot of superstitions, and get the believers focussed on the few aspects of the religion that may actually benefit society. Rather than squabbling over unprovable details that only divides people.
Personally, as an agnostic, seeing all the believers about me, has made me question what do they sense or perceive that I don't? I'm not so interested in the details because here's no way to disprove or prove them. But their living by a moral code, has encouraged me to be more introspective, to reflect on my actions and motives, and to... how can I put it?....find the better part of me. Still looking.