Ask HN: Open-source code with no license in portfolio?

I'm basically in the position where I feel I need to have a portfolio to have a chance to find anything better. Now, whether or not a portfolio should consist of decent but stupid code slapped on github seems up for the debate. However I'm having trouble starting projects that share this bubble between "of interest to me" and "willing to give away". I wondered if code needs to necessarily be open-source licensed if I have it open to the public. At least github seems to force it (does it?), I guess self-hosted would help with that.

Reason I'm asking is because most of the stuff I'm really interested in is code I might end up wanting to use for commercial purposes, like game and game engine code, audio libraries and shaders. Is it unreasonable to put code on the internet and expect at least some control over it? Or am I making it harder for the good guys to use the code (if by chance that would happen) while the bad guys are just going to nab it anyway?