Bear in mind..
That this is the USA definition, which also includes 16 and 17 year olds as "Children", where just about everywhere else in the world, at 16, you're age of consent and just about the most pent up age bracket.
Having friends of all ages, I'm hearing that 13 and 14 are now pretty much standard ages for things starting to get pretty physical in Europe (not sure about the States, I don't know as many people there).
What Stalman's quotes didn't cover was the specification of where he didn't see a problem.
If he was saying "I don't see a problem with a 50 year old bedding a 10 year old", I'd be having VERY strong words.
If he was saying he didn't see a problem with a 20 something and a 17 year old, hey, bit of a gap, but I don't see the problem, as long as it's consensual. 17 is plenty old enough to know what the world is about. I didn't have many illusions at 17, and things have only progressed to remove even more illusions from the current teens.
In fact, I'm thinking this is classic about what's actually wrong with the modern approach. There's absolutely no attempt to work out a frame of reference, and work out what someone was attempting to convey. Instead, it's a race to find the extreme outliers that can be cherry picked out of context and used as a central argument to crucify someone. It doesn't matter what they really said, what was intended, or motivation, what matters is what you can project onto what they said, and how you can manipulate that to fit your own agenda. The more sensational, the better, as sensation sells.
In my younger days, I used to hold dinner parties, where we'd discuss all kinds of topics, in depth, and appreciative of nuance; great debates were had, and they were extremely interesting times; I learned a lot from them.
These days, come even anywhere near a nuanced issue, and all you tend to hear is "You can't say that", or an immediate projection of completely the wrong end of the stick and someone railing against it.
Basically, it's just a mass weaponisation of logical fallacies, and is completely covered in the tactics of manipulation and disinformation ("Bad News" covers that very effectively in their gamified study, details at https://www.aboutbadnews.com/ ).
And yes, I've had to talk to some very vulnerable people in my time. I treat that as one issue, and Stalman's quotes in another. I'm certain of the context of a vulnerable person, and what's led up to it. I treat that appropriately for what it is. I'm unsure of the framing of Stalman's quotes, so I'd ask more to establish what frame we were dealing with.
The concept of whether a willing 16 or 17 year old should be sexually active (which in the US qualifies as child) is something completely different. When dealing with that issue, I frame it correctly in the appropriate context and then go from there.
What I don't do is say "There are vulnerable people who've been abused by people in power, therefore all consensual sexual relationships of 16 and 17 years olds are bad".
You are hugely correct though in that academic is only part of the picture. It's a useful guide. But as the quote goes, "The difference between theory and practice is that in theory, there isn't one, but in practice, there is."