the help states
The Watch tab in the Data Viewer requires that you log in to an account that has full access privileges to view expressions.
there area cases where you might want a senior or even in-house developer to be able to work on or test a system WITHOUT the ability to change the schema, as you wish that part of the process to be under a change control
To allow debugging (script debugger , data viewer) seems to fit into the same category as Allow Printing, which should be an option to allow or not.
It strikes me as much more dangerous to give a user Full Access than than be able to fully see the data viewer