Oh please let's not encourage UA to limit a system because of the bad actions of a few. I have gifted miles and upgrades to friends and family over the years - some had a FF# but many did not. One of the benefits of the program is the ability to share my love of travel with others. Often we would be flying to the same place but point of origin was different so on different flights.
Well run organizations have the rules for the many who want to do the right thing and not the few who want to game the system. You deal with the few differently (that is the role of management). Think sick leave policies. Well run organizations provide unlimited sick leave with no need to provide a medical certificate as employees are adults and treat them as such. Organizations that limit the leave and require medical certificates are treating their employees like children and they will act that same way. I have worked in the latter organizations where employees "plan" their sick days as the rules make it seem like an entitlement rather than what it is - if you are sick stay away.
I like the current UA rules, do not abuse them and applaud United for getting rid of the few bad apples.