The problem is that it doesn't require any physical presence
Changing the firmware on a device you own is a very sensible feature. This opens the road to alternative firmware images with new features. Or image that remove misfeatures like yellow dots with the serial number printed on every sheet. (some printers do that)
Maybe in the future printer manufacturers decide to print ads on their consumer printers, just like we have mobile phones displaying ads today. (maybe this will be sold as a feature against dried in print heads)
The big point is, you don't own hardware you cannot decide what software runs on it. Installing different firmware is no bug, it's a feature. And with technology becoming a bigger and bigger part of our lives, it becomes more and more important.