The blocking feature will build on the concept that the less exposed to negative speech users are on Reddit, the more they will want to engage with the community. That is important for the company, based in San Francisco, which aims to spread far beyond the 243 million unique monthly visitors it currently serves and break into the mainstream consciousness, much like a Facebook or a Twitter — with a similar ability to command online advertising.

The blocking tool could also serve to curtail the spread of online abuse beyond Reddit’s walls. Vitriol on the site can sometimes erupt into larger memes, spilling over into social media and other avenues and creating further repercussions. That behavior is also stoked by other digital haunts that are the favorite of trolls, including sites like 4chan and 8chan.

Reddit’s influence goes far, said Anil Dash, a web entrepreneur who has worked on blogging platforms like Livejournal. A post on Reddit is “similar to one tweet, embedded anywhere, and how it can travel very long distances,” he said.

Others have less faith in Reddit’s ability to clamp down on the Internet’s noxious elements, especially given the amount of time it took the company to take on abuse in the first place. Reddit has long been home to racist, misogynistic subcultures in areas called subreddits — small, topic-based forums where users can discuss whatever they wish. In autumn 2014, Reddit users traded stolen nude photos of celebrities like baseball cards, all organized in a subreddit.

“When you’re just now addressing the easiest solutions, it doesn’t speak well for what Reddit’s priorities are,” said Brianna Wu, head of development at Giant Spacekat, a gaming studio. Ms. Wu, who describes herself “a frequent target of the kind of abuse they are trying to stop,” was the recipient of many threats in 2014 because of comments she made about women in the video game industry.