Consider: "We will terminate your verified status for adding links to one of our competitor's sites."
(Source: I took a forensic linguistics course as part of a comp. linguistics program. One of the case studies we looked at was lying-- the data sets were comparing legal cases where documents were available that contradicted testimony, like the Enron case.)
Edit: Here's a research paper that talks about it: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4981627/
The passive voice was used to write this sentence.
Fun fact: That detector uses zombies!
It is a common and stubborn misconception that laws like these somehow do not apply to big (international) tech companies. It is more the product of cultural acceptance of a reality that has existed for long time. Maybe you are right about this, within the USA. But than that would say more about the legal reality within the USA, rather than globally.
Saying you can't post links to other services may be distasteful, but shouldn't be illegal in any reasonable legal jurisdiction.
In other words: these rules need to be explicitly stated in whatever contract consumer and provider agreed on.
These rules also need to be universally enforced. Rules that are (intentionally or not) written in such a way that they lend themselves for arbitrary application (that is, not equally amongst all consumers) are legally unenforcible. Therefore should be considered null and void. Which then leaves the service provider without any legal justification for their actions under contract law. That's at least how it works in many places, at least outside the USA.
If you want to limit the ways your service (or product) can be used, you can do so by explicitly arranging these limitations through a contract. Things that are already (otherwise) illegal do not have to be included in this arrangement (hopefully for obvious reasons).
Whatever is not explicitly forbidden by either law or contract, are not valid grounds for treating consumers differently.
Sadly, and mostly for historical and cultural reasons (and law enforcers not paying attention for a long time), it is often assumed that these rules do not apply to big service providers (and software producers alike). However, I have never found any legal basis for why such companies should be treated any different than any other one.
That Instagram uses the information gathered from providing these services for different services provided to another type of client (businesses, since consumers are officially not allowed to do business), does not change that.
But it could mean that Intragram is breaking laws that protect consumers (or citizens in general) from abusive practises. For example invasion of privacy (in particular surveillance), which is in many countries a privilege/monopoly limited to governments (just as use of violence).
When social media companies declared that privacy is dead, they essentially said that they do not acknowledge this monopoly/privilege of governments. This has been reality for some time, which is why many people got used to it and have accepted it as normal. However, just as criminals can claim that laws do not apply to them, the claims of social media companies might not have any legal basis. Maybe they have in the USA (I really do not know), but they sure appear to not have it in other parts of the world.
If Instagram stands by their decision to block third-party links, then they should phrase it as, "we block third-party links", not "they're not currently supported."
Well that's one way to phrase it.
1. "Links asking someone to add you on another service are not allowed on Instagram."
or
2. "Links asking someone to add you on a service not owned by Facebook are not allowed on Instagram."
"Support" vs "allowed" seems to me to be a distraction from the universality of that policy.
That's some weasel-wording right there. "Not supported" makes it sound like this is a feature they'd need to code that they haven't gotten around to yet. It's not -- they needed to take the time to explicitly block something that would otherwise work by default.
Phrasing it as "Links asking someone to add you on another service are not allowed on Instagram" would be more honest, but also make it obvious what they're doing. So instead, they go out of their way to phrase it as something out of their control rather than as a deliberate policy.