A few scientific results and blog posts based on them can be found in the comments, to clarify the issue and present evidence.
What could this mean in practice? A fictional but in my experience realistic example of a fellow plusser's stream of consciousness follows:
"I came to look at your Google+ stream planning to circle you. I found, among other things, that a few days ago you posted a 'joke' about asthmatic / blind / deaf / demented / diabetic / dyslexic / epileptic / [insert any other group with a disability and/or chronic illness] people. Seeing that 'joke' I decided not to circle you, after all. Because when I was younger I experienced quite enough of schoolyard bullies (and some teachers) who thought that my disability - or that of my brother's or that of my best friend's - was Such A Hoot. That wasn't funny then and it isn't now.
And I won't speak up about this in your stream - I don't want to deal with your multiple buddies, who commented because they found that joke SO funny. I will just quietly fade away."
In other words: outgroup jokes about people, who are worse off than you regarding some aspect of the joke, can easily give a similarly unflattering impression as that Big Bully hitting smaller kids.
Finally: if losing potential followers and future friends is not that important an issue for you, kindly refrain from commenting. Commenting on posts that are fundamentally uninteresting to the commenter too often leads to unnecessary strife.
no, I don't collect people on G+, circles and communities take care of that. They also set up a sort of self policing that keeps divisive humor at a minimum. With the exception of children and trolls nobody is very mean here. This isn't Facebook, no matter how much someone tries to use it like facebook.