Do you know what spring rates you will fit at the front?
The requirement for a roll bar is, in part, related to the stiffness of your front springs. It does not follow that what others have done is what you should do!
If they are already stiff and you add an ARB you will have a very rigid front end, and may end up removing the ARB.
I removed the ARB from my Cabrio (same chassis as a Sportster) and found it gives a much more supple ride, but still corners very well.
I found the seats are are so low that body roll is not really an issue - unless you plan on doing a number of track days with it?
Carry on without one - you can always go back and fit one if you feel it is really necessary.