Hello Attila
Just to clarify, you are referring to the rule in the Ethernet standard that says that if a device with autonegotiation enabled is connected to a device that has its speed and duplex manually configure, the autonegotiation cannot correctly determine the speed and duplex settings of the other device. As a result, it will default to half-duplex mode and to the lowest supported speed (10Mbps) to avoid potential collisions and to ensure connectivity is established. However, as you correctly stated, this is definitely undesirable!
However, I would not resort to manually configuring all of my interfaces with speed and duplex settings. The administrative overhead needed to do this is not worth the effort. It is rare that you would come across such a situation, however, if you did, you should have an NMS system that will detect it. Once detected, you would rectify it and all is well. This is a much cleaner and less labor-intensive solution in practice. Does that make sense?
I hope this has been helpful!
Laz