So many people already think The Mail Online swipes content from other sources that it can’t be libeled, new court papers charge.

The UK-based Mail Online sued Gawker in Manhattan Supreme Court in September after the gossip site published a scathing, first-person piece by a former Mail freelancer titled “My Year Ripping Off the Web With the Daily Mail Online.’’

But the Gawker writer was just echoing popular opinion, the website’s lawyer claims.

The Mail Online “has suffered no harm to its reputation, its goodwill, its business or otherwise as a result of the alleged defamatory or disparaging statement . . . because [the website] is libel-proof as to the subject matter of the article,” Gawker lawyer Susan Buckley said in recently filed court papers.

In other words: “What that means is that the plaintiff’s reputation is so bad, nothing that the defendant says could hurt that reputation,” said legal expert Daniel Kornstein.

“It just means that the reputation is so low for one reason or another that there’s no damage,” added Kornstein, a Manhattan lawyer who specializes in First Amendment cases.

The Mail has sued Gawker, saying the essay by James King was entirely false.

The Mail Online’s lawyer did not respond to a request for comment.