And while I hate using recaptcha, I also had the even more unpleasant experience of watching a forum that I moderated die under a crushing assault of spam bots that were smart enough to make it past the built-in CAPTCHA. Recaptcha isn't there to solve problems for the people who interact with it, it's solving problems for the people who chose to put it on their site.
I wrote in a sibling comment what value Facebook's login brings to the sites that opt into it. (Offload all the work of password handling, claims about stolen accounts, preventing sockpuppetry and catfishing, etc).
But there should be accessibility laws to prevent government agencies from blocking access to citizens/taxpayers using these proprietary technologies.
I don't know offhand of an open-source captcha library that's nearly as effective as reCAPTCHA. All the old "wavy lines through slanted text" ones are completely broken with current OCR techniques.
Gmail spam filtering? Isn't particularly good. I run my own email infrastructure and I get way less spam through it than on my gmail address. And I don't do anything particularly special other than configure postfix correctly.
Recaptcha? Was there ever a more hated piece of user abusive technology? Plenty of rage against it here in many discussions. I won't do business anymore with any site that won't let me buy without identifying 27 traffic lights in slow motion (looking at you adorama). We're all better off if this dies.
Facebook verification? Don't know what value this brings to anyone other than FB.
Youtube? Granted.. Hopefully with bandwidth costs reducing over time, decentralization becomes more viable.
Paypal? Always pay with credit card directly. The regulatory consumer protection for that was well in place before internet commerce even took off.
The original potential of the internet was in its fully decentralized functionality. Usenet being a great example (owned by nobody, hosted peer to peer) which should be studied a bit more now that we have generations of developers coming up never having known it. Of course, it was (mostly) overrun by spam. But unlike email where spam is pretty much defeated, there was never a meaningful effort in addressing spam on Usenet (forums and mailing lists took over instead). Applying the same techniques to NNTP could well be equally successful.
If there is any desire to avoid the internet becoming fully a new cable-tv controlled by just a few major player we need to pursue research into decentralized services as a priority.
(If nothing else, consider at least running your own email infrastructure if you're technically capable. Keep the foot in the door so it doesn't close permanently.)