If someone is pushing a "nonsense agenda" on others, be it a specific religion or atheism, then it's okay to push back politically. However, that is not what Dawkins is saying here. Dawkins just hates religion in general as the quote I posted above attests.
Considering the impact religion has on society in general and how they constantly push their agenda, be it about same-sex marriage, evolution, abstinence only sex-ed, or the pope telling people that condoms are worse than sex, I think a general 'pushing back' against religious claims is warranted.
People are of course allowed to believe and think whatever they want in their own homes and heads as much as they like, but when they make those ideas public, be it through conversation, on a forum, in the media or other channels, their ideas are open to criticism, ridicule and mockery, and it follows that if one supports a ridiculous idea then one leaves one-self open to ridicule as well.
As mentioned earlier, sometimes there isn't a discussion to be had.