I don't think the idea of proportional response is ludicrous in and of itself. For example, I support the laws stating that if someone pushes me out on the street, I'm not justified in shooting them. Generally every state says I'm only justified in using deadly force (outside my home) if I'm confronted with what I perceive to be deadly force. (Obviously that perception is likely to be scrutinized afterwards.) I think that's a reasonable law.
In my home, the Colorado law actually states “any occupant of a dwelling is justified in using any degree of physical force, including deadly physical force, against another person when that other person has made an unlawful entry into the dwelling, and when the occupant has a reasonable belief that such other person has committed a crime in the dwelling in addition to the uninvited entry, or is committing or intends to commit a crime against a person or property in addition to the uninvited entry, and when the occupant reasonably believes that such other person might use any physical force, no matter how slight, against any occupant.”
That also sounds like a reasonable law to me since it's restricted to actions inside my home. It also sounds reasonable to me that Colorado extends this doctrine to include my vehicle, where I should have a reasonable expectation of safety, and the ability to protect myself from deadly force.
It also sounds reasonable to me to extend this doctrine to RVs, since it's my "home" for the time I'm in it. Even more so than a normal vehicle, it baffles me how some states do not extend the same protections I have in my home to my RV. My life is no less valuable and the potential threats are no less real just b/c this home has wheels.
But the idea of proportional response is ok with me outside the home as it prevents public gunfights over silly things.
"Duty to Retreat" inside the home, on the other hand, is absolutely ridiculous.