But it just seems so contradictory. The US is one of the biggest polluters of greenhouse gases on Earth yet it feels it needs to import European and Japanese cars and then "gimp" them to bring the power output down by 20 or 30hp, all supposedly in the name of "emissions standards"
There's no "supposedly" about it. That's just what happened. Carbon dioxide was not the particular emission that the European cars were failing to keep in check in the United States by the late 1970s. Carbon dioxide is directly tied to fuel mileage, and the United States government by and large did not consistently care about fuel mileage until Obama was president (and other than occasional specific years the populace certainly never has). What the United States government cared about was
smog; hence why the US went so far as to carve out a specific exception to allow CARB to set its own, even-higher emissions standards because it was so bad in California. That's why catalytic converters were basically required on US market and Japanese market cars starting from 1975; whereas they weren't required in Europe for nearly two more decades.
That's also why diesels were never popular in the United States; since in addition to usually being more expensive with more expensive fuel they tended to be dirty in a specific way that the United States government didn't like (remember who it was who found out what Volkswagen was doing) and the fuel mileage benefits didn't mean anything in a country where nobody cares about that to begin with.
I never remember the UK or Japan having gas thirsty monsters like that. Nowhere close.
British marques, just like German and Italian marques, were perfectly capable of making things that were just as piggish on fuel as American cars from the 1970s. And both of those cars notably also had quite a lot of problems actually getting to the US market as well. The XJS V12 had 10% of its power lopped off the top each time Jaguar redesigned its engine. A US V8 Vantage is a regular V8 with a Vantage body kit and interior and none of the performance; and emissions troubles eventually got so bad that Aston had to withdraw from the US market entirely only a few years into the life of the Virage.
I can't believe that the emissions spewed out by a 1973 Skyline GT-R would be anywhere close to those. Or a 1976 Ferrari 512BB.
A 1973 Skyline is undoubtedly for all intents and purposes just as bad as an equivalent 1973 Challenger. There's not much point in splitting hairs when it comes to early 1970s performance engines; and that's a major reason why those two engines (the S20 engine in the GT-R and the Chrysler 340 engine in the Challenger Rallye) were both gone before 1973 was even over. A 1976 Ferrari 512BB (a car never sold in North America just like the early Countach wasn't because Enzo Ferrari didn't want to even try making it emissions or crash test compliant) is
undoubtedly far worse for emissions than a 1976 Trans Am 455.
I personally think there's another explanation and that is the government does not want to saturate the US car market more than is necessary with non-US marques in order to keep GM, Ford etc competitive and viable. And I honestly wouldn't blame them. The first duty to any government should be to work in the interests of its citizens and products.
That is why there is the 25 year ban and the Chicken Tax and the briefly-implemented Reagan administration voluntary input restrictions; but it had nothing to do with why you couldn't buy a 911 Turbo in 1983. If emissions issues weren't such a big deal at the time Porsche and Ferrari and Lamborghini and Mercedes Benz wouldn't have had so many problems meeting them while the Japanese marques (who had similar regulations in their home country) could generally breeze through them. But they did, and it hurt their image for decades for the public to know that they were being sold a lesser car than was available elsewhere. The United States was by far the biggest single market for the kind of cars those companies were selling (especially in the Reagan years) and those marques still regularly skipped out on selling certain cars here completely or offered extremely compromised versions because that's all they
could do. Early fuel injection systems bootstrapped onto engines designed for carburetors that still retained them in Europe throughout the 1980s. Compression ratio drops. Engines downsized beyond the point where it actually makes sense for the application.
US market-specific engines with power numbers just as bad as those of the regularly maligned domestic cars.
One
cannot overstate how hard it was for even the large European manufacturers to meet US/Japanese emissions standards throughout the 1980s when they didn't have to bother with anything similar in their home markets; and inability for the smaller European companies to do so
regularly led to them withdrawing from the US and Japan entirely every time the engine they had hitched their wagon to to sell cars with stopped meeting emissions standards. In the US market there was no 959. There was no F40 (the Federalized model didn't come out until near the end of the car's production run in the 1990s). There was no 288 GTO. There was no V8 Vantage Zagato; or even a real version of the regular V8 Vantage. You had the Countach 5000QV, which impressively even in federalized form still produced over 400 horsepower. You had the Testarossa, which in the US was admirably only
very slightly downrated to 380 horsepower. You had the 911 Turbo when it returned to the US market in 1986. And you had a C4 Corvette if you ordered the B2K package through your dealer. Those were the four most powerful and fastest cars you could buy in the US in the 1980s; and none of them were available before 1985. There was no pre-fender flare Countach. No variety of Berlinetta Boxer. No 911 Turbo. The most powerful Corvette had 205 horsepower. I don't see how you can consider how having an entire region of the world where manufacturers who specialized in performance cars didn't have to deal with any of that stuff for two more decades than the ones in other countries did as anything but
extremely beneficial to them.