User Specific columns are secure in the sense that each user has their own version of the values, and it’s literally impossible for any user to see the values of any other user. And the only way you as an App Builder could see the user specific data of your users would be “Viewing as” that user in the Data Editor.
They are not really meant for the use case you have in mind.
A better approach for your scenario is to have a separate “Public Profiles” table that is a mirror of your main User Profiles table (without row owners), but excludes any private information that shouldn’t be shared. And then apply Row Owners to your User Profiles table.
Bob Petitto has a good video tutorial on this. I’ll dig it out and add a link shortly.
Update: here you go…