You want an answer from the user but would select a default.
That is absurd.
Most users get through a form as quickly as possible.
Often they will skip a field with a value just to get through the form or they may have been distracted and when they come back to the form they just assume any field with a value they completed.
It proves the value came from the user. They cannot say - I did not select that.
OK to the defaults is not the same as selecting the defaults.
If most of the users were a the lowest level role and that was the default then maybe.
You would only error on giving them less authority than required.
Still rather than come back and fix it later - make em pick it up front.
I guess default to the cheapest form of shipping would also be OK.
In the final total they also see it as a line item.
And when they are spending money they are more likely to care.
If this is an administrator that you know will answer the form properly / completely and have asked for a default and the default is "no harm" value then OK.
I have an app with a predictive algorithm and admins said they want to see the prediction and just accept it if it is correct and they will change it if it is wrong. We said OK because they are admins and they get feedback as to when the prediction is right or wrong.
For a lower end user we don't show them the prediction as we fear we will get what we call compliance coding.