More and more, I'm coming across sites that expect me to login to use their resources, or to even view them.

So, what happens if I don't have a Facebook account, or a Google+ account, or whatever account they expect all web users to have?

What is their relationship to FB/G+/Twitter/LinkedIn/etc., that these site owners feel compelled to collect my user habits on the login providers' behalf?

I understand the usefulness of a federated authentication process, e.g., OpenID or OAuth, but for you site owners, is your content that important and proprietary that you're willing to lose viewers by forcing a login with a specific identity provider?

I had a FB account at one point, as much a work requirement as for personal use, but, as expected, it absorbed too much time from my life, plus FB would change privacy settings with little notice to users, and I'd have to repeatedly review all the settings to determine what's changed. Plus I found myself dealing with people who felt compelled to tell me things I really didn't care to hear or see - you learn new sides to some people you thought you knew. 
Anyway, I nuked the FB account years ago, and don't miss it at all. None.

It just PO's me when a site owner, whose content really doesn't necessitate being locked, feels that I must first login to access their site. The one at right came up for an article on seasoning a cast iron pan!!!

Farcebook's (FB) been adding to the disconcerting movement to require access to what was either previously public or should be public information. If you have a public FB site, you should be complaining, a lot, e.g., the screenshot below is from a museum that offers high-quality exhibits and performances. They've operated a FB page for a lot of years, but now viewers who don't have a FB account (I'm one) get the bottom of their screen cut off by this obnoxious message:

Facebook login overlay on public page

I left FB several years ago (& I don't miss it) due to their objectionable policy and configuration changes (for FB's benefits, not their users), and now even "public" sites are being commandeered by FB's autocratic management.

Yes, if you scroll down the page enough, you're provided an option to "Not Now" as far as signing up for a FB account, but that's only after this message grows in size, and the "Not Now" appears in small print below everything else.

It's obtrusive, obnoxious, annoying....And it's wrong. This is not what FB users signed up for, and what they've come to expect from their "public" pages.