If you put something in the public sphere, it is public. Simple as that. You have no right to turn your intention of how I "ought" to consume your product into forcing me to do so if you have given me your product for free.
Use a paywall, Use proper authorization.
I solely use firefox for getting around paywalls. I have it automatically clear all cookies upon exit. That way any website that gives a few free articles per month will always be free for me.
From an economics perspective, they are trying to using old school pricing tricks (e.g. bundling, price discrimination, variable unit pricing to enable 2 article users == free, 10 articles == paid) as a tool for managing their customer funnel. But the golden rule of price discrimination is it only works if you can actually prevent your customers from engaging in arbitrage and can keep them in their bucket. A store can have a policy like "limit 1 per customer" but that doesn't prevent me from getting 100 of my friends from buying the thing. If I want to clear my cookies and look like some anonymous new customer each time, there is absolutely nothing illegal OR immoral about that. That's capitalism and they have designed a pricing model that can be gamed.
Sure, and if there's urban chaos, there's nothing preventing me from looting a store. Or sneaking stuff in my backpack. It's still stealing.
As to your example about the art, it's more like if one piece of art is in the window, but the rest of the gallery you can only see if you buy the ticket. But there's a door in the alley you can sneak in to and nobody will notice. So you sneak in the back, avoid paying the price, and get to see the whole thing for free. That doesn't sit right with me ethically.