The game's creators insist it doesn't "promote any sort of violence", but a promotional video features the player stalking a school and racking up an on-screen tally of two types of kills - "civs" and "cops".
"I want them to pull the game simple, just pull it", said Robinett. "This really crosses the line".
"Keeping our kids safe is a real issue affecting our communities and is in no way a 'game, '" he said.
The game is titled "Active Shooter" and slated for a June 6 release.
The game is receiving an outcry after a student shot and killed 10 people in Santa Fe, Texas.
The first-person title by Revived Games (whose credits include White Power: Pure Voltage and Dab, Dance & Twerk) isn't available to buy just yet, rather it's set to launch on the platform on June 6, but there have been calls for the game to be removed before it goes on sale early next month.
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Andrew Pollack, whose 18 year old daughter died in the shooting, told the Herald that the game's developers are "sick people", and that games like it would desensitize young people to the horrors of gun violence.
On Steam, the game is described as a "SWAT simulator in which dynamic roles are offered to players". There have also been plans outlined to add a survival mode, allowing players to step into the shoes of a civilian that needs to "escape or perform a heroic action such as fight against the shooter itself". "Why would anybody think it's a good idea to market something violent like that, and be completely insensitive to the deaths of so many children?"
In a statement, the game's Steam page says, "This is only meant to be a simulation and nothing else". "If you feel like hurting someone or people around you, please seek help from local psychiatrists or dial 911".
"The company is taking the stand that this game is legal because of free speech and everything else that tech billionaires hide behind when they are doing something the public knows is absolutely, morally corrupt but legally fine - but we can not stand for this", the website reads.
Acid noted that other violent games have existed on Steam's platform, including a 2015 game that involved killing civilians at random, though not in a school setting.
But Petty sees it differently and has already contacted the game store's parent company, Valve Corp.
In recent days, the publisher of the video-game marketplace, Valve, has come under intense pressure to cancel the game's release.