Maybe backdoor was a bad way to describe it? Maybe it's used as a customer-initiated support channel for when the customer wants the vendor to access the device.
USG probably would have had better luck if they pitched backdoors as a consumers protection measure and had a law mandating that:
1. Software companies must always have a remote and practical method to correct dangerous flaws in the software they issue.
2. To protect consumers' valuable records, all device manufacturers must back up all data on any device the produce. Such backups should ensure that the data is always accessible by the user even if the user were to lose their password or keys.
It would be a security disaster, and it already is.
Source: Fortinet admin