In cleaning and updating a database, it's often helpful to redefine UDFs and reorganize data. To that end, it would be helpful to completely hide disabled UDFs, such that the data is stored in an archival form, but not visible to users who are trying to make use of the new UDF. Having the new and the old side-by-side is begging for confusion and conflicting data.
I agree that it should be user definable whether or not to display the disabled field. We have disabled fields in the past temporarily that we didn't want to display but later wanted to display them. We did this to "unclutter" information for a specific campaign.
I totally agree. There should be an option to display the disabled field or not.