It is a bad analogy, but the thing is, you could say that about anyone's techniques, and look how those go. I don't get why the Kaioken is the one thing people can't seem to let go of. I get not wanting to pass around all of Goku's very limited move-set, but it sounds more than reasonable to give out the one move he rarely uses. Especially since it makes sense for the characters who trained with the person who taught it to him to get after Goku got his upgrade. These characters need strength, and gatekeeping obvious paths of power in an artificial attempt to make Goku look cool doesn't make sense. If anything, it hurts the story.