It is entirely possible to use a Kindle for epub only (that is, never “buy” a book from Amazon). There are lots of epub around, including from places like Gutenberg.
Additionally, the Libby app allows you to use your Kindle in conjunction with your local library’s electronic collection, which (in my case) is quite sizable and allows you to “borrow” DRMd books for a finite amount of time.
Especially considering they were explicitly designed NOT for that purpose. Not only is it illegal for government agencies to deny you anything if you refuse to provide an SSN, but until 1972, this verbiage was printed on every Social Security card: “FOR SOCIAL SECURITY PURPOSES – NOT FOR IDENTIFICATION.”