[Anaraxes]

Lots of sources like to start by saying Seelie / Unseelie is not Good / Evil, and then generally fail to deliver. We have a natural bias toward law and summer. Dresden does this, along with lots of other fantasy.

Winter can be rational, cold, and calculating. That also includes "enlightened self-interest". They don't have to be selfish and exploitative. They understand Prisoner's Dilemmas and positive-sum games (a "win-win", where others can benefit as well as their own interests). They can also play the long game, giving up local advantages in the short term for longer-term or larger-scale benefits. Star Trek Vulcans are supposed to be cold and logical, right? But they're not portrayed as evil because of that.

If Winter is so rational, then Summer gets to oppose them by being more chaotic. Rampant and careless growth, not well-tended gardens of beneficial plants, weeds more happily than crops. Half-elves and changelings are most likely offspring of Summer, as they're the ones that will value sex and procreation over the well-being of their partners. That can extend to rape and "Mars Needs Women". Summer is into unleashing, exploring, and enjoying their emotions -- all of them, including greed, jealousy, hatred, and lust. Satisfy your urges now, consequences be damned. They're the ones that will provoke humans just to see what happens. They're the "men that want to watch the world burn".