There's too much character ownership on the part of some fans. I don't get the "Muppets were never supposed to be for kids, but Frog help them if they aren't kid friendly" paradox here.
By all means, a lesser show would just be a constant barrage of lame and obvious jokes stretched to the point of once shocking now redundant when everyone's desensitized. Something like a Robot Chicken skit. I'd even say something to the extent of Greg the Bunny, which I enjoyed, but now just seems like the same standard collection of stock adult jokes. While the show isn't extremely subtle, it's not the kind of immature adult "adult" programming you'd see out of some of the bad half of adult swim shows or that awful High School USA program.
The issues I find eye rolling are simple.
Jokes about the Mayhem being stoned. Yeah, that could easily turn into the same Otto from the Simpsons situation I mentioned earlier. OR, it could be that jazz musicians and pot have been a thing since the 30's. I SEVERELY doubt we're going to see Dr. Teeth and Zoot toking in any future episodes. My only issue with the joke is that the writers couldn't find a smoother way to work it into the script when they did it effortlessly in the prepilot. As long as it stays as an aside (which I doubt it would become more than that), I'm fine with it. Just no Flanderization.
Fozzie taking a souvenir. I find this the biggest overreaction. This is basically an innocent, down on his luck comedian that gets little respect and kinda picks up on it. What he did is a more innocent version of what a Seinfeld character would do (knowing Seinfeld, it would be George and he would have been out of spite). To me, it wasn't so much he did a bad thing as much as he did an impulsive thing and spent the rest of the episode twisting in the wind with about, only to make the same dumb mistake when he didn't get caught. Heck, he stole the same thing Jay stole from Carlin!
Zoot drawing something adult in an adult's birthday card. I'll agree, it was kinda awkward a joke to make, but the jokes more of a "we're all adults here, and who hasn't got a card with something lewd in it as an adult?" sort of way. Because that's the thing we need to remember. The characters are supposed to be adults. Adults in the entertainment industry. Even ones that work on kid's shows need to ..vent. Remember that New Zoo Revue "outtake?"
And above all...are we still really bugging out about Kermit and Piggy's relationship? They've found a nice angle that's not the repetitive fat joke/hai yah nor is it the "they were married off in MTM! End of story" blandness of a conflict free mutual relationship. And what it speaks is the language of nuance. They hide their true feelings from each other, Piggy acts out and lashes out at others, Kermit's clearly depressed, not comfortable as he thinks he is and suffers some PTSD from her freakouts. But make no mistake, the relationship is a key for conflict and plot points. If nothing else, seeing this spread out over the course of the series gives that continuity edge that past Muppet projects didn't.