Reddit’s creation of the blocking tool, which is available to all registered users, has not gone over well with all of its user base. When the site was founded in 2005 by Steve Huffman and Alexis Ohanian, college dorm mates from the University of Virginia, it took a laissez-faire approach to Internet commentary. The philosophy was to let forum members post almost anything they wanted and let the rest sort itself out.

As a result, any restrictions are considered an affront to the open aspects of community dialogue. On Wednesday, five hours after announcing the blocking tool, there were more than 2,300 comments in response to the feature. Some praised the move while others criticized it.

“The outcome then will be many subreddits where groupthink will dominate, and discussion will be suppressed,” wrote Donnadre, a Reddit user, in a post on the site discussing the new feature.

In an interview, Mr. Ohanian acknowledged that shifting the site away from some of its roots is hard. “People, generally, do not like change,” he said. “We have to do what is best for Reddit over all.”

The company has maintained that the number of nastier subreddits is minuscule among the tens of thousands of other subforums devoted to things like makeup, television shows or food.

The idea for the blocking tool is similar to a “muting” function used by Twitter, the 320 million-user social network that also faces criticism for the way it handles online abuse. When you block a user on Reddit, you will no longer see that person’s responses to your posts. That person will not know about the block, a strategy aimed at keeping them from simply creating another user account.

Some Reddit employees attribute the creation of the new tool to an infusion of resources, including dozens of new employees and more than $50 million in venture capital raised in October 2014. Last May, the company instituted a policy that forbade harassment on the site. Then in July, Mr. Huffman became chief executive of the company in a management shake-up.