I think it's more about being recognised as a section of society. A section who do not wish to give undue deference to religion, a section who does not wish to see crimes that would otherwise be considered hateful or bigoted being accepted as part of a persons faith. A section of society who do not wish to be absorbed into a default position of Christian, or CofE or whatever.
There are christians who accept these ideals as well. There are christians who see the benefit of a secular society where religion is private but protected. These are not solely atheist ideals, as if there are any.
Think of it this way. You start a not-golfer club where the commonality between all the members is that you don't like playing golf. As you can guess, there is a very wide range of beliefs and ideals amongst these members. Even more, not playing golf really isn't a cause or something that is pursued. You then write a manifesto telling these members what they believe and don't believe, and it really has nothing to do with not playing golf. I think you would cause people to scratch their heads wondering why such a manifesto is needed.
I don't think this article represents dogma, but rather an attempt to write down a series of principles which, the author thinks, represent a common thread in atheists/heathens or what ever you choose to be called.
Getting atheists to agree to anything is pretty hard. I think the only thing we do agree on is our love of bbq kitten.