May I suggest that if they never bothered to file a U.S. tax return this is the least of their problems.
Actually for most people that this catches, this is their ONLY problem. Most dual citizens do not actually owe any US tax. Their tax returns would be one zero owing after another. This is because for most individuals US tax rates are lower than Canadian rates, and so the tax credit for Canadian taxes paid will invariably wipe out any US tax owing. Every year.
However, since this is a penalty on FAILURE TO DISCLOSE, rather than failure to pay taxes owed, it will catch even people who never, ever would owe a cent of tax if they had filed.
It's one thing to have draconian penalties on unpaid taxes, basically nailing tax evaders. It's quite another thing to impose draconian penalties in cases where there are actually NO taxes owed, just based on arcane and not well communicated disclosure requirements.
Note that there are some people living in Canada who are US citizens, but who are only vaguely aware that they are. People who have never worked in the US, in some cases never set foot in the US, and never applied for any sort of US identification. However, if they have two US parents, or if they were born in the US to parents who were there only temporarily, they are citizens--and this rule applies to them--even though they have never lived or worked in the US, and do not hold a US passport, SSN, or any other US identity document.
I heard a guy on the radio talking about this. He immigrated to Canada back when US law was that if you became a citizen of a foreign country you lost your US citizenship. He had assumed ever since then that by becoming a Canadian citizen he had ceased to be an American. He'd always believed that for the last 40 years or so he had held only a single citizenship--Canadian. Well the IRS didn't agree...