In the movie Memento, our hero Leonard has a very short memory. Teddy, a friendly cop, promises to help him achieve his goals. But Leonard has a Polaroid of the cop in his pocket, with the chilling legend: DON'T BELIEVE HIS LIES.

As Sprint and T-Mobile reportedly come to a merger agreement, I keep flashing back to Leonard and Teddy. Softbank's Masayoshi Son, who holds a 70 percent stake in Sprint, is the cheerful, helpful guy who's appearing at Americans' elbows promising to lead us to a land of better broadband if we'll just kill a competitor for him. But he's counting on us having a short memory, and little critical thinking.

I've written before about why a Sprint/T-Mobile merger is a bad idea. You should re-read those columns (especially if you're an FCC commissioner.) But I wanted to specifically address some of the themes Son has been on about in the past month or so.

Son's central argument is that home broadband access in the U.S. will soon be dominated by three giant companies: AT&T, Verizon, and KableTimeCast. He's right. That's going to lead to high prices and fewer upgrades, he says. He's also right there. But buying T-Mobile will not help him fix this problem; it will just help him eliminate a competitor.

You Can't Do Home Broadband Over Just Cellular
Sprint is a pure cellular wireless company. So is T-Mobile. Cellular technologies can't deliver the capacity that U.S. home broadband users want. And buying T-Mobile doesn't get Sprint any closer to providing that greater capacity.

A few years ago, AT&T told me that the average American home consumes 21GB of data per month. It's probably more than that now. Sprint has been laying in more capacity with its "Spark" network, but it's been dialing back its home broadband service plans, not expanding them. The company's Clear subsidiary used to offer unlimited home wireless broadband, which Sprint killed when it moved its old WiMAX network over to LTE. With Spark, Sprint doesn't offer any plan larger than 12GB, and that costs $80 per month.

For more on why Son's promises are impossible, read Kevin Fitchard's definitive column, where he lays out how this merger couldn't possibly offer the capacity American homes need.

Rather, as Fitchard says, ground-breaking wireless broadband networks will come via Wi-Fi, white spaces, and other technologies that buying T-Mobile wouldn't provide. If Son is looking to improve home broadband, he's merging with the wrong company.

Softbank offers home broadband in Japan, true. But it's through a wired, land-line connection, not via wireless. If Son wants to shake up the home broadband market in the U.S., he should be buying CenturyLink, other landline providers, WISPs (wireless ISPs) or radical new startups, not T-Mobile.

A Merger Won't Expand Sprint/T-Mobile Coverage
Sprint and T-Mobile's other weakness is in coverage outside major metro areas. As we've seen year after year in our Fastest Mobile Networks studies, Sprint and T-Mobile do well in large cities, but outside those areas, AT&T and Verizon tend to dominate.

The reason is that the smaller carriers, until recently, lacked the low-band spectrum that can cover large distances. T-Mobile recently bought some 700MHz spectrum, and Sprint has been converting its Nextel 800MHz spectrum to help fix the problem.

But merging the two carriers doesn't guarantee better rural coverage and could actually make the situation worse, because the FCC is looking at tilting the upcoming 600MHz auction in 2015 away from AT&T and Verizon in the name of helping smaller players. With a merged Sprint/T-Mobile, there would be no nationwide underdogs, and AT&T and Verizon would have a better chance at using their deep pockets to snap up all that spectrum.

Furthermore, let's remember we've been here before. AT&T swore up and down that it would only be able to cover 80 percent of the country with LTE if it didn't get to buy T-Mobile. After that merger was rejected, somehow AT&T found enough change in the seat cushions to make plans to cover 97 percent of the U.S. population.

Another merger between large wireless carriers will have no positive effects for consumers. It's just going to take us to Canada: a cozy, closed market where three big carriers exist in a comfortable equilibrium.

If Son really wants to disrupt Internet access in the U.S., he could look at buying CenturyLink, Dish, Comcast, or creating the next great white-space ISP right at home in Kansas City. But his insistence on T-Mobile shows that all he really wants to do is to reduce competition. We know where that leads: higher rates and lazier companies that don't have to strive to provide great service.