Valve have decided they've had enough controversies over what games should or shouldn't be on their platform - Steam. This question came to attention due to two controversies of late - Active Shooter and White Power: High Voltage.
Valve and Steam didn't have any clear lines drawn when it comes to the games on their store. There is no rule that would prohibit games such as Active Shooter or White Power: High Voltage from being released on the platform. This resulted in controversy when the games, both made by the same developer, were removed as people started asking on what grounds Steam banned them.
While it's evident that Active Shooter was a cash grab aiming to profit on its shock value of shooting up schools, Steam didn't have any strict rule in place to ban it. The game game was removed following broad media coverage and consumer outrage, but Steam now states that this is not the reason for the game's removal as they claim that people have falsely assumed that "these decisions are heavily affected by [Steam's] payment processors, or outside interest groups".
The situation apparently caused major confusion, not just for customers and developers, but for Steam's employees as well. To that end, they assumed a rather weird position by stating "If you're a player we shouldn't be choosing for you what content you can or can't buy. If you're a developer we shouldn't be choosing what content you're allowed to create". Basically, they chose inaction.
Valve "clarified" this statement by saying they will allow everything into their store, except things that are illegal or "straight up trolling". On the other hand, they will also make filters more visible and available so Steam users can protect themselves by choosing the type of content they want or do not want to see.
Developers will also be getting similar tools as Valve feel that developers who create controversial content shouldn't be harassed for doing so. There is something terribly wrong with this policy though. Something about not having to deal with the consequences of people's own actions.
Apparently, Valve have a disclaimer now, stating that the items in Steam's store "will not be a reflection of Valve's values". Therefore, if someone develops a game such as Active Shooter, it doesn't mean Valve support or find it to be acceptable, but it will remain on Steam store. You can read the full maze of Valve's statement on Steam.