Facebook announced steps this week to crack down on groups using its site to sell guns, including prohibiting them from posting offers that "indicate a willingness to evade or help others evade the law."

But some gun safety advocates say the new requirements from the world's largest social media site do not go far enough.

"We’re not thinking of this as a victory," said Will Villota, communications director for the Brady Campaign to Prevent Gun Violence. "The bar has been set by other social platforms like Google+, Craigslist and eBay -- they do not allow, will not allow, unlicensed sellers to post guns for sale on their communities. We think Facebook fell short of that bar."

Facebook can "formalize its policy to outright prohibit" these kinds of sales and can commit to using a technical solution to block these posts, he said.

The restrictions and requirements that the social media network announced Wednesday are not proactive enough, Villota said, even when it comes to barring minors from viewing such content. Under the rules announced Wednesday, Facebook would prevent users under 18 from seeing posts identified as selling firearms if they are flagged.

But Villota said such posts should be screened ahead of time.

"Even the age-gating relies on reporting," Villota said, "If you don’t report that post, it’s not going to be restricted to shield minors from that content."

Nor was he satisfied with Facebook's existing policies. "Facebook has gone so far as to prohibit paid gun ads, but not posts from unlicensed sellers," he said. "That’s a huge inconsistency."

Facebook, as well as platforms such as Yahoo's Tumblr and Google's YouTube, have had to walk a narrow line when evaluating how much input they should have in censoring content. Facebook places more restrictions on content in ads. But when it comes to what its users are saying on their own profiles and pages, the firm has said repeatedly that it must balance free speech concerns against questions of when objectionable content should be censored.

With such a large community looking at content on the site, a Facebook spokesman said, the social network is also confident in Facebook users' ability to police themselves.

"With more than 1.2 billion in our community, we're the world's largest neighbor watch program," the spokesman said. "We encourage anyone who sees anything on Facebook to bring it to our attention."

The company is also taking pains to direct those whose content has been flagged for selling firearms to information explaining how the law may apply to their activities. When a user reports someone else's content as inappropriate for this reason, Facebook sends the poster to a Help Center page that outlines the responsibilities they undertake by agreeing to sell a gun online.

Other gun safety advocates expressed their support for the changes, including Sandy Hook Promise and Moms Demand Action, which worked with the social network to develop the guidelines.

Villota said that this is just part of a much larger issue, however. Online gun sales have enabled those who would have been blocked from buying guns after a background check to purchase firearms and use them in violent crimes, Villota said. And, he noted, many postings on online gun sale sites include descriptions that openly state that buying this way flouts state background check laws -- the sort of language that Facebook has specifically said it will not allow on its site.

Villota said that around 40 percent of gun sales are made online or through gun shows and that the Brady Campaign is continuing to call on Congress to close those exceptions in the law.

"Once that happens, that will exert much more pressure on sites like Facebook," to outright prohibit this kind of content on their sites, he said.