There are limits, content-wise, to what Valve will allow to be sold on Steam. In a rare (if short) public statement, Valve announced that the visual novel Rape Day (previously covered here) will not ship on Steam. Still, they're not making any change to their policies, and took the opportunity to expound on that, briefly. Valve state that Rape Day "poses unknown costs and risks", making it unsuitable for Steam, but reiterate that their role regarding moderation is reactionary - people are free to list what they will, but Valve reserve final judgement on what can and cannot be sold.
While I'm not surprised that Rape Day has been pulled from the store, Valve's seemingly renewed commitment to their (almost) anything goes policy has caught me by surprise. I was honestly expecting the company to alter or clarify on rules, setting hard limits on what is or isn't allowed. Instead, they've doubled down on the vagaries of their current system. While Rape Day was obviously pushing boundaries for the sake of shock value, developers still have little idea of what is actually allowed or not. The game, deeply distasteful as it was, technically did not violate any rules as defined.
While broadly preferable to the dark ages of Steam where developers had little way to know whether they'd be able to sell on the store, the current system is still opaque to developers and customers. If a game has generated sufficient controversy as to make it seem unpalatable to Valve, they can just pull it from sale. While the concern over Rape Day was sincere, I fear this is a system ripe for abuse, and if the press can be manipulated into railing erroneously against something for long enough, I fear Valve will react as they have here. Clear rules would solve so many problems here.