To go along with Heaven's post, general education plays a large part. Some people possess the intelligence to intuitatively distinguish valid from non-valid and strong from weak forms of argumentation, but most of the general population needs to be educated to sound methods for doing so. A lot of people can't even idenfity circular logic. I faded about 3 years before I went to college, but when I finally took "Logic and Critical Thinking" in school, it really helped me put words and methods to some of the ways I had previously evaluated arguments and gave me some new ones.
We're not just fighting the control of a human institution masquerading as Christ's substitute, we're fighting human nature as well. Our brain protects us from many hurtful situations in our past or present. Though many of us confront our manipulation by the Society, I'm pretty confident most do what I initially did when leaving, which is the basic "fight or flight" survival mechanism. You may initially think you're going to "fight" it, but once there seems to be no way to realistically "fight", we got away as fast and as far as we could. The mind further protects us by refusing to think about or dwell on the past. (Though that's hard at first if your family and friends refuse to speak with you.)
That survival mechanism works the same way while you're still in the organization, and it isn't just because the Society conditioned us to think that way. Once we make such a life-altering (and at the time, a seemingly carefully considered) decision to join up, our brain tends to bias or ignore anything contrary to our decision. On top of that is the Society's direction to ignore the "fight" when it comes to apostasy and fleeing from it. It's very hard to get past that, but not impossible.
If I were going to put up a billboard, (particulary if I wanted to direct people to a website), it would not relate to anything doctrinal or a known controversial JW subject like blood and dying kids. It would be a statement that is borderline unbelievable, such that it gets someone's attention (possibly makes them laugh), and stays in their mind long after they drive by, hopefully telling their friends and aquaintences about it.
Something a little too over-the-top would be: (Jehovah's Witnesses EAT BABIES!) theotherwhitemeat.org
I know that sounds crass, but with todays blitz of media and advertising, it really takes something outrageous to get people's attention. Especially if they're trained to ignore it. Once to a website, anything presented has to be as some of the other posters mentioned. Primarily a list of facts and experiences. Let people draw their own conclusions. You get a lot further in persuasion if the other fellow thinks he came up with the conclusion on his own instead of trying to cram it down his throat.
More ideas later, gotta go work.
