Make sure to disable the Auto-Updater. That will try to run anyway, and will probably muck stuff up if you are not logged in.
People ask for this occasionally, but though there are workarounds. Plus, running it as a real service can be meddlesome, for most users, since you
do need access to the "real" server copy of MC's UI (at least occasionally for the things the client copies can't do). So, it would be a niche user thing, and I think it is just not real high on their priority list.
I mentioned once that I'd love to see an "Advanced" or "Server" edition of MC, which could be for more money, that would offer this and other server-type features (multiple user control, for one), but they basically weren't interested in doing something like that at this time. There are other fish in the sea that they want to catch first.
Plus... I don't know. Not logging into a terminal is the most trivial of security precautions. I'm not even professing to be that skilled, but... If I have unmonitored, physical access to your machine? It could probably be owned if I put my mind to it. Someone with skills could
certainly do it (without blinking). So, why not log it in and set it to lock the screen immediately? If you are ultra-paranoid, use a randomly generated password (stored in something like LastPass of course) and change it regularly. Put it inside a VM and isolate it. I don't know... It isn't like MC is the only useful application that has this issue, so...