Even in 2D drawing the ViewCube can be helpful in orienting the drawing, but if you really want to disable the ViewCube when you start a new drawing, read further for the solution.
When you start a new drawing, AutoCAD uses a template (DWT). To change the ViewCube setting for new drawings, you only need to edit your template(s). Word of warning it is always a good thing to make a backup of existing files before overwriting them, just in case.
Click the start New button (or the AutoCAD command QNEW).
Great feedback from R.K. McSwain to not use QNEW but the Open command..
I would suggest using the OPEN command to open the desired DWT file instead. If you use the QNEW (or NEW) command to open a new drawing based on a template, you could accidentally save that over a different template, and that will be a problem.
When the drawing template opens, at the command line set the system variable NAVVCUBEDISPLAY to 1 from the default of 3.
Now you just need to Save the drawing as a .DWT (template) and overwrite the existing template.
And just like that the ViewCube should be gone from your display on future new drawings. You would need to do this for all of the templates you normally use.
This common question was identified, and a solution sent to me from my Autodesk colleague Dan Kuhmann of the AutoCAD Test Development team. The AutoCAD Test Development team receives a great deal of bug reports and feedback and some are common and we can point out solutions to help you such as this one. Thank you Cliff!