What you propose is equivalent to not locking your house when nobody's home, or buying an expensive sports car and then modifying it to use a push start and not need any kind of key to either get in or start the car.
There are ways that this can be made kind of secure (namely, turn off all remote access and all network services provided by the system, which also means you cannot share files from it over the network, among other things), but that still doesn't deal with the issue of physical security.
Now, before you start on the same kind of comments you've made on other answers about the computer being in a personal residence, I would like to point out that that is not even remotely good physical security unless you either keep the room it's in locked whenever you're not in it or never have any guests at your house. The fact that you've got no password means that accessing the system requires no more effort than being in the same location, and unless your paranoid or a social recluse, it's rather likely that you have more than a few people over at your house at times and do not always know exactly where each of them is.
And this really reinforces why even having a bad password is important. By just having one you prevent people from just casually accessing your system. For most people, just that tiny bit of extra effort is sufficient to prevent them from even considering trying to access your computer without your permission.