Plenty of countries have national parks btw. Many of them had them before America.

Well not really though ? Yellowstone established in 1872 is generally considered the first national park, in the modern sense of the term*, and inspired others to follow in the next couple of decades in Canada, New Zealand and Australia. It wasn’t until the 1900s that the first national park was established in Europe.

* there are a couple of other places that also claim this distinction, depending on how exactly you define what a national park is, but not many

Calling national parks “America’s best idea” is a quote from historian and environmentalist Wallace Stegner - I think the point of it is not to toot some US exceptionalism horn - in context it’s more of an acknowledgment that America deserves a lot of criticism - saying that national parks are America’s best idea is actually putting a bit of shade on other American exceptionalism claims, especially during the Reagan “shining city upon a hill” era.

Didn’t the original full body scanners used at airports use backscatter X-rays, which are ionizing radiation ?

I believe these were mostly replaced by millimeter-wave scanners, and are not used anymore (even banned in some countries) but a lot of the initial pushback and debate surrounding the scanners when they were first introduced was about potential health risks of repeated X-ray exposure from those scanners, and so the idea of ionizing radiation exposure persists to this day in many people’s minds.

I first got on the Internet just as the shift from :-) to :) was happening, only geezers still used :-) and :) was the hip new thing…

I am not sure you were as wrong as you think - see definitions 2 and 3 here

Usage of words shifts and sometimes expands over time.

More references here or here

I would personally definitely interpret “apparently” and “plainly” differently - “apparently” to me is “the evidence so far does seem to point this way, but I am not necessarily convinced, or have strong feelings either way” vs “plainly” is “the evidence is clear, I am convinced, and so should you be” - although obviously context would matter as well and could alter this interpretation.

Edit: even your example usage “I’ve been trying to get myself out of that habit, but even judging from my comment history, it’s apparently pretty hard” - to me the usage of “apparently” here indicates similar tension and/or contradiction, in this case between belief/intent (I am trying to stop the habit) and evidence (but my comment history shows otherwise) - it wouldn’t work quite as well with “plainly”

It would work with “evidently” but carry more of a connotation of confirmation and shift the emphasis (I am trying to, but it’s hard as confirmed by evidence) rather than contradiction (I would like to think I am doing it, but evidence shows otherwise) - of course you might have meant it either way (or even neither) - I am just saying how it reads to me.