Long ago, many people who used Blogger would login to Blogger using a link in the navbar - or a similar Blogger login wizard.
Long ago, people who logged in to Blogger, using the Blogger login, had no need to worry about "third party" cookies and filters.
When blog owners logged in under Blogger, the dashboard worked transparently.
Everybody could use the Blogger dashboard and some Blogger features, such as full page and popup window comments, without any problems. A login cookie, created under "blogger.com", could be read under most Blogger features - such as a full page or popup window comment form, or the various Blogger dashboard components - without any thought to any "third party" cookie filters.
Not everybody understood the difference between the dashboard and blog features.
The lack of worry about "third party" cookie filters, with Blogger login, did cause some dissent. People able to use the Blogger dashboard in general, became rather skeptical, when told to allow "third party" cookies, to enable the Stats "Don't track ..." option, or maybe the embedded comment form - or various other Blogger features.
Some blog owners, when advised to change form placement, because of reader problems when publishing comments, might object because the full page or popup window form lacked features - but not all. A few objected, simply because they did not believe that cookie filters could be so capricious.
Some blog owners attributed the differences to poor design.
Occasionally, some owners would ask why the embedded comment form would be designed so negligently, to require third party cookies - as if Blogger intentionally designed their features, to make it difficult to use their service. At one time, the embedded form was re written, to use "blogger.com" content, embedded in an iframe - possibly to allow the CAPTCHA form, for embedded comments, to avoid the nefarious "third party" cookie filters.
With Google "One account", Blogger and Google, instantaneously, has made the entire Blogger service require enabling of "third party" cookies. If a login cookie is created under "google.com", it will need to be read under "blogger.com" (the Blogger dashboard utilities), "blogspot.com" (Blogger blogs, published natively), any country code aliases that might apply, and any Blogger blogs, published to custom domains.
There is no more confusion about "third party" cookie filtering, because some features may work, and other features, mysteriously, don't work. Now, all of Blogger (GMail, Picasa, YouTube, ...) will require "third party" cookies to be permitted, if a login cookie is to be consistently accessible - and all services are to work, reliably.
All problems are not caused by cookie filtering - and this expands the confusion.
Yet, "third party" cookie filters alone, do not explain all Blogger feature problems, that do involve cookies, in some way. Both the recently explored comment wizard CAPTCHA form, the interstitial warning displays, and the Reading List disappearances - all have other, complementary, issues.
Cookie filtering is just one detail, in the Blogger infrastructure - though when problems are seen, one should check and correct the filters.
Hopefully, as the need for third party cookies becomes more uniform in Blogger, everybody using Blogger can become objective enough, and stop inappropriate filtering. With third party cookie filters less critical an issue, maybe Blogger Engineers can identify the problems that they can, and should, solve.