The game's Steam forums are dominated by threads calling for the developer to reconsider and for Valve to do something about the game, as well as people criticising Valve for the fact that it gives the boot to many games containing nudity while letting the likes of Active Shooter fester on digital shelves.
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".
The father of another Parkland victim, 14-year-old Jaime Guttenberg, has urged consumers to boycott the game in an emotional series of tweets.
The website touted, among other things, its "realistic first person controller", "impressive" artificial intelligence, and "real life situations" in the game.
It was developed by Revived Games and published by the company Acid, which has said it plans on selling the game for $5 to $10 on the video-game marketplace Steam and releasing an alternate "civilian" mode.
Needless to say, the timing couldn't be worse: just last week, a school shooting took place in Santa Fe, Texas - the latest in a host of school shootings this year.
However, on the game's page, the developer said, "please do not take any of this seriously".More news: James leads Cleveland Cavaliers to finals
And it's not the first time the developers of this game have made games with attention grabbing titles.
Players playing the role of the shooter will be able to earn "game stats" such as how many police officers or civilians they kill.
This sentiment is shared by the Steam gaming community, viewing Active Shooter as offensive and distasteful, as well as incredibly detrimental to both the platform and the gaming community at large.
"This is only meant to be the simulation and nothing else", the website reads.
Valve, itself, did not create the game, but it is providing the platform for people to access it.
Acid added that other games that have been released "literally focuses on mass shootings/killings of people" in a way which Active Shooter does not.
"It turns my stomach it makes me sick to watch it", said Stephanie Robinett, a mother of three who heard about the game. "If you feel like hurting someone or people around you, please seek help from local psychiatrists or dial 911".
Gilliam says parents should be tired of their children playing any active shooter games, even if the research doesn't directly tie them to violence.