There are public sections of G+ and private sections. If you have a private album limited to 4chan buddies or whatever with tubgirl, goatse, the lemon party, etc. and they took that down, I would find issue with it. But if you've got goatse as your public profile picture, that is an issue that Google has to deal with. I use those examples not because they are directly comparable to what Siegler put up, but because I imagine most of the people here on hn would find those images offensive.
When you're dealing with a really massive user base, you're inevitably going to have a lot of people that would find an image of a guy flipping the bird to be horribly offensive (their heads would simply explode if they ever saw goatse). Should you cater to those people? Where do you draw the line? Do you go with the U.S. Supreme Court's definition of obscenity? Siegler's picture is certainly not obscene, but it would certainly make a prude think twice about signing up for G+. I would rather not cater to the prudes of the world, but if Google wants every person with access to the internet on G+, then they'll have to offer some concessions to them.