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In order for users to validate charts and graphs that they are building in Tableau Desktop they need access to the record-level data. So far as I know (and I've tested this) it's not possible to simultaneously enable users to connect to a data source in Tableau Desktop or web editing in Tableau Server/Online whilst preventing them from working with the underlying record-level data.
Just to to show how ingrained this notion is in Tableau there are several ways in Tableau Desktop besides Export Data to CSV for users to see & copy out the record-level data: users can view data in the data grid in the Data Source window, view data from the Dimensions menu and copy that, view data using the tooltip or right-clicking on marks from a view they build, create a view where the viz Level of Detail (based on the dimensions in the view) is record level, and/or create a view and turn off Analysis->Aggregate Marks and then copy the data from there. (Not all of these are implemented in web editing).
So you'll need to use one of the options in the link that @Meenu provided to limit users, or (worst case) just not give them Tableau Desktop access at all.