Spot on.In BSAC we teach the OOA diver take the octopus regulator as the other dive would otherwise have to notice what is happening, comprehend it and act. We do not tell divers never to actively donate if they notice early enough.
The logic behind the secondary take rather than donate is to reduce the time lost for the donor to comprehend what's happening and then act. The time for a diver trained to primary donate to comprehend the situation is the same. Therefore, secondary take is quicker and doesn't have the potential of placing the donor diver without an air supply.
My biggest bugbear is the way a lot of AS regs are secured: by hose retainers that don't allow quick release, or stuffed into pockets, and even just left hanging. I use a magnetic clip and demonstrate the ease of deployment before every dive. It allows me to confirm I haven't been knitting when kitting up.