Given modern copyright law the real problem is actually kind of the opposite, which is that by declaring no licence you are making it legally impossible for people to use your code at all.
> Yes, without any license, your code defaults to falling under copyright law.
> In that case, legally speaking no one can reproduce, distribute, or create
> derivative works from your work. You may or may not want that. In any case,
> that's only the theory. In practice you'd find defending your rights to be
> difficult.
I am sure defending your rights in this case is no problem, assuming you have enough money. If you don't have enough power to enforce them, the same thing could probably be said about using licenses as well.
I can get behind the core idea though, which is you should always pick some license. It isn't that hard to do these days, anyone using github should easily be able to understand the basics of at least the GPL, LGPL, MIT and BSD licenses if not from reading them directly then from the very many summaries of them easily available on the web.
At the very least, publicly declare your code is in the public domain. I realize there is much debate on whether public domain even legally exists as a concept anymore in many countries, but at least such a declaration acts as a strong signal you are okay with me using your code.