Would you refuse to visit websites that force registration even if the account is free?

Yes, I already do. I don't visit Instagram because you need to login to view posts.

What's all the fuss about, you don't care?

I definitely care.

Is advertising a necessary evil in fair trade for content?

Ah, now this is an interesting question. I can certainly see an argument that ads are necessary to support "free" content, although personally in many cases I prefer to pay a subscription to support content rather than being subjected to ads.

Really though this is kind of a red herring because it's predisposing that violating your privacy and collecting personal information is a prerequisite to serving ads. It's required for individually targeted ads, yes, but they don't need to traget ads to the individual, they could target the ad by site or the contents of the page hosting the ad.

Would this limit your visiting of websites to only a narrow few you are willing to trade personal details for?

I would not visit any site that sold my details to an advertiser.

Is this a bad thing for the internet experience as whole, or just another progression of technology?

Yes, this is very bad.

Is this no different from using any other technology platform that's free (If it's free, you're the product)?

There's a reason I don't use most "social media" sites.

Should website owners just accept a lower revenue model and adapt their business, rather than seeking higher / unfair revenues from a privacy invasive practices of the past?

Yes, or find a different revenue model that doesn't invade people's privacy.