It doesn't matter if the workbook is packaged or not, Desktop is the authoring tool used to create/edit reports (workbooks). Tableau Reader can only read/view packaged workbooks and this is what is normally used by report consumers.
Now, I'm sure Tableau wouldn't mind all of your users BUYING A LICENSE for Tableau Desktop. If money is a factor for your company then the FREE Tableau Reader is a smart choice Remember, you can set up filters & prompts to help allow the users change some things.
Also, you don't want users to open workbooks you're working on because of conflicts -- you make a change and save it, they change something and accidently save it, thus over-writing your work. Not a good idea
If you just gotta give your users the ability to change reports, and you have a lot of users, then look into Tableau Server. You'd set the user's permission to Publisher and then they could hack away at the report to their heart's desire.