It's usual to declare where you are staying, it isn't usual to have to register with the local authorities in every place you do. I do accept it, countries have different rules and cultures. Foreigners do end up breaking such local rules when going abroad, including the Chinese. But doing so shouldn't result in being banished from the country. Imagine driving into Austria without a toll sticker and no longer being able to get a Schengen visa. Of course we don't know the full story. Hopefully this is more about the authors situation than something that will become commonplace.

It may be annoying or inconvenient, but China is not the only country a requirement to register with the local authorities. The fact that it applies to all types of visas may throw some travelers off. Still, it is their responsibility to make sure (preferably before arrival) that the requirements for entry are met.

When you break the rules (intentionally or not), you're taking a risk. Some people get off unnoticed whereas others learn the hard way. Ask people familiar with the country and its laws before arrival and plan your trip properly.

So whenever you visit a country then you spend several months reading up on all their local laws? Do they even have an official English version, or do you hire a translator? Here's a question for you, what's the Chinese law regarding the use of a VPN/proxy? Does the law differ based on when/where you used the VPN and what it was used for?

The sexual relationships is relevant because foreigners in China have a reputation of sleeping with a lot of girls, and this leads to a lot of resentment from many of the Chinese. If they at the airport can so easily see when/where a foreigner stayed at an AirBNB, then you have to wonder what other info these people, as well as the embassy people approving VISAs, can see. They do not need to give a reason for denying entry, so it seems it's only a matter of time before they're provided with even more private info that will most definitely be used against foreigners.

Well, usually I will ask friends or colleagues who have experience of that country. But if not then yes, I will spend an evening reading up on the country and its rules/customs while planning my trip. I don't know a sensible traveler who doesn't.

Spending an evening reading up on the country may result in you becoming familiar with the punishment of insulting the Thai king, or the risk of engaging in protests or anything political in China, but that's about it.. regarding China, you can't even Google the laws concerning VPN/proxy. You even give an example yourself of you failing to read up on the rules. There are millions of laws, many of which are not even available in English. You can't possibly expect people to become familiar with countries laws.. that would take months and you could still get fucked for no reason. People rely on common sense, and common sense tells you that if AirBNB is available in X country and you have no problem booking the apartment, then that's that.