> I do not want a future employer judging me on the basis of the half-finished amateurish experiments I knock off on my free time as I'm learning a new language or messing around with a new framework or just screwing around in general because I'm bored.

In this case there's no need to publish this type of code; Github offers private repositories for free. If one is convinced that there is value for other people from half-baked experiments, it's definitely worth publishing them in the open (it's possible that they're valuable), but if there isn't, why doing it?

I also notice that many people display private commits in their profile stats; this way, one can signal the amount of activity, if they want (within the limits of what's possible, as certainly commits don't necessarily correlate with intense activity).