Usually I start by discussing effectiveness, or lack thereof -- so I've practiced explaining why they don't work and the actual risks in ways that everybody can understand.
Sometimes it's better to start with the safety risks (which is something I'm pretty credible on because I was on a National Academy of Sciences panel on dependable software). If it's a small-government person or fiscal conservative, I'll emphasize the cost. Or I'll discuss the dignity aspects, phrasing it in terms of the government's policy to take a naked picture of every traveler and choosing 3% of them to have their breasts and genitals groped.
It often takes several iterations; don't be frustrated. And of course there are plenty of people who just won't be convinced, in which case my usual strategy it to stay in their face enough that they consider changing their position just so I'll shut up about it already :-)
I have the utmost respect for Ben Franklin, but this quote is not his best work. You might not be realizing it, but you are giving up liberty every day in exchange of something you find more valuable. Examples include signing up for credit, giving your address or social security in exchange of discounts, using a card at your grocery store or local mall, etc...
There is really nothing wrong with giving up some liberty just as long as 1) you're clear on what you're getting in exchange and 2) you agree that the deal is fair.
How large is the group of people who think it isn't wasted effort?
I recently had a conversation with a group of well-traveled, well-educated people who honestly believed that the new scanners and pat-downs are okay because they are designed for our own safety. The 4th Amendment was never a concern to them. When I brought it up, the answer was essentially that the end justified the means. Ben Franklin's famous words[1] did not convince them otherwise.
How are you (general) educating people about their rights?
[1] http://www.quotationspage.com/quote/1381.html