Richard Dawkins at a recent conference for atheist, told his followers to mock Muslims and Christians for their stupid beliefs!
Source please, with context. There is a big difference between challenging someones beliefs and criticizing them, and as far as I've read, Dawkins has always encouraged the former, not the latter.
As far as Singers beliefs, your quote is taken out of context and doesn't represent his actual beliefs, as cantleave's post points out.
Also, be very careful about grouping atheists together in one lump... It's like grouping all theists together...