Look people: as much as we would like a movie, or any production for that matter, only include strictly a cast of Muppets, they wouldn't be able to pull it off. If it were a cable special, like, say, Muppet Musicians of Bremen, or Emmet Otter, that'd be one thing, but in this case, the Muppets alone aren't going to be enough to bring in the masses (not just Muppet Freaks, but the public in general), they pretty much have to rely on some star power to really pull 'em in. Now, whether some people like it or not, Ricky Gervais does possess that kind of star power: he's relevant to mainstream media right now, as a writer, actor, and comedian - in fact, he's responisble for what was America's biggest hit for a while: The Office, as he was behind the original U.K. version of which the U.S. version with Steve Carell was adapted from. Now, if all the hubub is over him being an atheist, think of what Jim would do. Jim was all about inclusion: he hired white, black, straight, gay, righties, lefties, and I'm sure he hired religious and irreligious; so it's not really a matter of whether or not an actor is Christian, Jewish, Atheist, Agnostic, Muslim, Buddhist, Scientologist, etc, it's whether or not the actor is good enough to carry the film along... I think Gervais can carry the film along, and I give him the support and trust that I, unjustly, denied Jason Segel in the previous movie. Plus, Gervais is part Canadian, so that automatically gets thumbs up from this Canadaphile.
Now then, as far as the human cast, in general, goes... they've only announced, what... three human leads thus far? Three? And that's some how too many? Think back to GMC again, the main human cast consisted of Lady and Nicky Holiday, as well as Nicky's entourage of three lady spies... that's five humans in the main cast of a Muppet movie. Think to MTM: there was Pete, Jenny, and eventually Ronny as the main human cast, there's three. The Muppets (2011): Gary, Mary, Veronica, Tex Richman, and Jack Black... that's five again. And of course, most of the Muppet movies are known for their countless additional celebrity cameos. So, like, what's the deal with humans in the sequel?