So, many comments here target US or Trump in particular. But in fact, as many noted, there is not real connection – it started long time ago. Also, I bet, there are quotas (e.g. number of people) to be detained, so they have to fulfil it.
Also, US is just an example here (because many conferences are held in the US), but also there are stories from the UK, for instance. From my point of view, the problem is that with social networks it is extremely easy to get access to your whole life – it is already pretty easy to identify person on the facebook, for instance (right now there is no way to prove that it is _exactly_ you, but I am pretty sure they will be soon). So, with restrictions on such monopoly media (and I've heard it is already harder to register on the Facebook), it is very easy to end up in a situation where we will get "human score" (similar to credit score, but in the digital world), which will be used in such situation.
And even the bigger problem is that it might be needed for a work, for a loan application, etc, so you wouldn't be able to do all this without it (or even "to apply for a visa your score should be higher than 3.0". My predictions are that governments will try to work more closely with popular platforms trying to emerge such (there were few stories than people were detained because of tweets) metrics, and to broad access not only from your phone, but from their device, just your user profile.