As an atheist who fits, to some degree, both of your two categories, I'd like to point out something that I have long observed in the realms of atheist thought, but more often, in the realms of religious apologetics.

First off, I've encountered very few atheists who are not also agnostic. This is not a contradiction, it's a very strong philosophical proposition. We don't know that there is or is not a god, but extraordinary claims require extraordinary evidence. Theists, even with their often elegantly twisted apologetics, have yet to offer that extraordinary proof. Sam Harris is not an outlier. Men like him, and myself, have no problem admitting that we cannot disprove a negative. It is literally a basic tenet of logic. However, in almost all cases, we can disprove just about any organized religion. Usually from it's own works. Most of us do not engage in this too much, because of point two. The one that just about all theists either cannot wrap their head around, or refuse to. I do not know which it is, but I suspect the latter.

This point is not subtle, but for some reason, Theists see it as such.

If you tell me you are a Christian, or a Hindu, or a Muslim, or that you follow the B'hai faith, I will have a good idea of what you believe in, and be able to discuss it with you. Hopefully without heat, but that is rare among Theists.. But the point remains. The label informs me and others of the core of your belief system.

When I tell you I'm an atheist, this is not true. It does not tell you what I believe. It does not tell you whether or not I believe in a spiritual world, it does not tell you if I am a moral or ethical person, it does not tell you anything at all about what I believe, only what I do not.

This shouldn't be a difficult concept.