A newly-joined, never a JW here. And I must admit--you're absolutely right. How are we to know? Much like JWs waking up, unless there's a reason, most people won't look any further than the superficial, which is where JWs excel. I have only known (or been aware of knowing) three or four Jehovah's Witnesses in my life. Usually it's come up over the birthday issue and it's telling that's that the only thing most people will know about them, not their "lifesaving" teaching. The few I know are intelligent, moral and generally respectful people. But I finally met one that made me curious as to what JWs really believe (a boy...isn't it always?). He was "raised as a JW", not particularly active but still indoctrinated (no birthdays/holidays) and goes to the Memorial and some Kingdom Talks, but I doubt that part. Through him, I also learned of its hypocrisy: that just because you're a JW doesn't mean you're living right (read: they're like everyone else so how can they claim this superiority and exclusivity?).
As I investigated more, it made me really discouraged and distraught. They weren't just another Christian (albeit legalistic) group. I should also mention that like James Mixon said, I attend a church that warned that JWs are a cult but before my investigation didn't know exactly what that meant besides legalism. Of course, legalism itself can be harmful and is ultimately futile (Colossians 2:23, Romans 10:1-4; Romans 14). But it's enough to say that my feelings were very conflicted. I went between anger, frustration, despair, and compassion. Anger at the wrong doctrine, manipulation and dogma that only they hold the truth. But equal to that, my heart broke because, for the most part, these are people who are seeking God and want to please Him.
So yes, non-JWs don't understand, but we can learn to. HB is another great example of this We can learn to care especially if we're given a reason to. That's where ex-JWs come in. Your stories matter. What I've read here and other sites has truly shocked me and moved me to action. Knowing what I know now, I do what I can to get the word out. I live in NYC and see many of the "apathy" carts/tables littering subway platforms in major stations. I'm pretty sure I'm a thorn in their side at this point but when I have time, I keep at it. So know that you have an ally.