I personally don't think they are responsible for societies attitudes, but what they did is basically show a younger or more susceptible audience (because let's be fair thats all that listen to Brand):
"Hey look, its alright to be ****s to people you don't know, as long as its funny".
It's a negative spiral that only goes down.
If that's the case he's also responsible for sexual promiscuity, the fall in numbers of people voting, the secular society and people wearing tight fitting trousers. Every week his broadcasts make reference to all the above but i'm yet to see a thread condemning his influence on those matters.
I think the majority of people (and that includes younger audiences - a little patronising?) are a little more intelligent than you give them credit for.