Justice Paula Feroleto of the Erie County Supreme Court said 25 plaintiffs could try to prove that the social media platforms were designed to addict and radicalize users, and gave Payton Gendron knowledge of the equipment and training needed for his racially motivated mass shooting at Tops Friendly Markets.
The 25 plaintiffs included store employees and customers who witnessed the May 14, 2022 shooting, and the son of one of those killed. Gendron was 18 at the time.
In seeking dismissals, Reddit and YouTube said they merely hosted third-party content and were not liable under a federal law governing such content, Section 230 of the Communications Decency Act, or the U.S. Constitution's First Amendment.
But the judge said the plaintiffs could try to show Reddit and YouTube owed them a duty because their platforms were defective and led to injuries.
She also said the mental distress that many witnesses suffered from the "horrific" attack was a "special circumstance" justifying their pursuit of negligence-based claims.
In a statement, Reddit said hate and violence "have no place" on its platform. It also said it constantly evaluates means to remove such content, and will continue reviewing communities to ensure they are upholding its rules.
The decision's timing appeared unrelated to Reddit's initial public offering, which is expected to be priced on Wednesday.
YouTube spokesman Jose Castaneda said that the platform disagreed with Feroleto's decision and will appeal.
He also said YouTube had "deepest sympathies" for attack victims and their families, and tries to find and remove extremist conduct while also working with law enforcement.
The lawsuits were filed by the gun control advocacy group Everytown Law, and seek civil damages.
"We must hold accountable every single bad actor that prepared and equipped the shooter to target and kill members of Buffalo's Black community," its executive director Eric Tirschwell said.
Other defendants include Alphabet, Google, retailers that allegedly sold firearm equipment and body armor to Gendron, and Gendron's parents.
Gendron pleaded guilty to charges including murder and terrorism motivated by hate, and was sentenced in February 2023 to life in prison without parole.
He also faces federal charges, and the U.S. Department of Justice said in January it plans to seek the death penalty.
