How could they assure there´s an atheist dogma if non of its components exists?
As far as the formal definition of atheist goes, there is no dogma associated with it.
But in a2k discussions/debates, atheists generally identify themselves with methodological naturalism. That is the world view that everything has a natural cause and that explicitly excludes any supernatural beings or forces. That is as close to atheist dogma or religion as it gets.
Im sure there are atheists here that will say 'You can't box me into that definition' and of course they are right, But I'm talking about the ones who usually join into the threads with theist/religious themes.