The regulations being overturned here are ones that have only recently taken effect, and non-anonymized, non-aggregate selling of ISP data is still outlawed by the Cable Communications Act of 1984, which protects subscriber privacy is 47USC § 551.
Put simply, neither the most recent executive order, nor a reversal on Net Neutrality overturns that law on the federal register.
Of course, if Congress were to draft a bill that does so, the current fears would be well justified.
Legally, I can't think of a case where it's been tested that didn't lean the government's way, so who knows?
Repealing the Obama rule does mean that you can't opt out of data collection or sale. It does not mean that your individual browsing records are available to anyone with enough cash. Moreover, much of the rules Trump's executive order overturn had either very recently taken effect, or not yet taken effect.
There may be much theoretical damage from overturning the regulations, but the practical effect here will be minimal, and limited because of the other laws that already exist to prevent exactly the doomsday scenario many are predicting.
I'm not saying that Trump isn't after your privacy rights, but the surest test of that will be whether or not he goes after or seeks to circumvent the 1984 protections I referenced earlier.
I think it is truly insane.
I do agree. There are somethings you can do to mitigate things. But at some point you have to be you (e.g., FB, etc.) and as small and minor as such digital breadcrumbs might seem, they add up.
I don't know anyone who would fault me for not being on Facebook (yes I know this has a strong selection bias). Only time was at a convenience store, looking a bit puzzled I had to scan my ID-card in some device (to buy cigarettes), the guy explained this was announced on Facebook, I (completely neutral, matter-of-factly, already having complied with the ID-device thing) replied I don't have an account on Facebook which he took as a cue to start some anti-privacy diatribe at me. My guess he was probably having a bad day, possibly from other people giving him a much harder time about the ID thing. I finished the transaction, excused myself because I (really) had to catch a bus, and wished him a very nice day.
My point is, when I look around, it seems like Facebook is going the way of the cigarettes. The majority of people (that I know) know of at least one or two scandalous things that are deeply wrong about the way Facebook treats privacy and manipulates its users. Of those people, a good chunk hate it, really want to quit, but feel they can't due to social pressure or addiction. Just like cigarettes. Others make excuses about convenience, little vices, relaxing. Just like cigarettes.
I don't know how many of you are old enough to remember that you could smoke in trains, bars, in restaurants while people were still eating 2 metres next to you. As late as the early 90s. And only after those bans people started to dare to ask if you could maybe smoke outside, in home situations, even if they're the guests and it's your home (I was younger and inconsiderater).
If you don't remember you maybe also don't remember how thoroughly ingrained the social act of smoking was in society. Only a few decades ago, nobody could imagine where we are today. Smoking was just so normal, even if you didn't really, you would occasionally, your friends would offer, people just liked it too much, were addicted too much.
The almost-entirely-non-smoking-everywhere society we have today was seen as an impossibility. We could never get there, we couldn't change or impose, people wanted it too much. And it was a hard transition before it got momentum, but it did in the end. I personally, as a smoker, welcomed these bans, because I figured it would make it easier for me to quit (hint: if you're addicted, you still have to quit by yourself. those bans maybe helped me the first 5% of quitting).
The point is, it may seem impossible to imagine a way out of this anti-privacy swamp. But it's not too late. Just remember the cigarettes and how far we got. DON'T let anyone tell you it's useless to refrain from using surveillance tech X just because "you're going to be tracked any way because P, Q and R" (being your phone, CCTV and the NSA). The fight is NOT lost, not at all. It's just getting started, now that people are slowly realizing they don't actually really want this, they are mostly made to want this, and more and more people want it to stop, and it would help if only everybody else would stop shoving it in their face.
Just because it seems impossible now doesn't mean we should roll over, curl up and stop voicing your dissent, ever.
Then maybe our kids (or other people's kids--who didn't ask for this either) can grow up in a society where they're not quite as pervasively tracked and surveilled as our generation.
If it helps maybe to imagine the next impossible thing, imagine everybody securely wiping the exabytes of private data they've collected on us so far. I really can't see that happening either and it kind of gives me hope in a weird "wishing on a star" kind of way, because other important things used to seem just as impossible.
 I've quit since. It's hard. Very hard. Unfathomably harder for some people than others. I will never judge an addict in my life.
47 U.S. Code § 551 (c)(1)
Except as provided in paragraph (2), a cable operator shall not disclose personally identifiable information concerning any subscriber without the prior written or electronic consent of the subscriber concerned
So this section of the law, though another might, does not support your statement that "that they could sell that (which is false)".
Your statement is too strong. It's not outlawed. There is a relatively easy avenue for ISPs to sell this type of data, and it's written into the law, and not some sort of weird loophole. It is voluntary that they have not pursued it on their part.