I agree with you, it's hard to explain. Here's a sketch of how to frame the discussion, just for fun:

WHAT WILL SOPA DO TO THE INTERNET?

The Internet is the Goose That Lays the Golden Eggs, and this bill wants to let Hollywood perform surgery on it. Every tech expert and internet company agree that this would be a drastic, disruptive shift. I say, the Internet's been working pretty good for [country] so far. Don't break it by putting more paperwork and gatekeepers in there.

HOW, IN LAYMAN'S TERMS, IS SOPA HARMFUL?

Imagine you're an entrepreneur. Your small business is disruptive and different and successful.

But your big, slow, powerful competitors get worried, and suddenly, your shop's lights and water are turned off. Crazier still, your shop is physically relocated back away from the street, with no signs and no way for people to find you. Your bank has closed your account and frozen your funds.

This is all because of a letter, not a court order. Your providers and suppliers and utilities, they got a letter that claims that you're infringing on other company's trade secrets. And the law says that they're guaranteed legal immunity, only if they stop doing business with you.

Most people would say that could never happen in this country. It'd be crazy!

But every reputable Internet expert, and every Internet company agree that this is what SOPA will do to the Internet.

SOPA provides incentives to service providers to shut down businesses based on unsubstantiated claims. And it could bring free-market innovation on the Internet -- the one thing America still does well, the one thing pulling the economy forward -- to a screeching halt.

WHY IS SOPA BAD FOR THE ECONOMY?

Making new internet businesses vulnerable to immediate and brutal closure (usually, for their user's actions, not their own!) unless they work out deals with Big Content in advance would be a terrible drag on innovation.

WHY WOULD THEY WRITE SUCH A BILL?

Because SOPA and PIPA are actually industry-wide power-grabs, a power-play by the Content Industry Dinosaurs to give themselves the keys to the tech kingdom under the guise of 'fighting piracy'. This is backed up by how google, Amazon, Facebook, Tumblr, Youtube and Twitter are all banding together with the Net Coalition. But the new, growing sectors of the economy aren't as good at gaming politics as the old, stagnant sectors.

The old sectors see disruption in their future, and this bill would give them the upper hand in negotiations for how people consume content. In the process, they would make themselves kingmakers and protection-money-collectors of startups and services that let users interact and connect in ways that could be claimed to be 'infringement'. Like sharing a link, or posting a youtube video.

WHY IS THE BILL SO WELL-SUPPORTED?

It's got scary, bipartisan support, because Big Traditional Business is for it on the Right, and Big Hollywood Labor is for it on the Left.

...

Just a sketch. ;) This is just for fun -- but if you want to explain it to someone, I think the shopkeeper-gets-shut-down analogy is a powerful one. Ever since Rick's Cafe getting shut down in Casablanca, or Jimmy Stewart's S&L, it's resonated.