This is about deceased people. We absolutely should not be posting Social Security numbers for living people. Although these numbers were widely and freely used in a public context in decades past, some time around the 1980s they started to be used as unique identifiers to connect a person to their financial records, medical information, and other sensitive items, and they are now highly protected.
Social Security numbers for deceased people are public information that appears in Social Security records that have been released to FamilySearch, Ancestry.com, etc. I have sometimes included these numbers in a profile (usually as part of the source citation) because they are unique identifiers that could help someone else find or identify the record, and because the number itself can indicate the region where the person lived at the time they obtained the number, and I think also the approximate time period when they obtained the number.