Um, If we evolved from primates, why do they have longer DNA then we do? Shouldn't it be the other way around if we did evolve from them? (Take that Mr. Darwin.) Back to topic, I think Atheists, much like people who choose a faith/path/whatever, like to think that their view is correct. (Much like most people) If they are confronted with spirituality, it plants a seed of doubt. They tend to avoid such things.
First off, it's totally incorrect to think that we evolved from modern primates. It's just as correct to say that they evolved from us in a way. In short, we all simply had common ancestors. Therefore it would be impossible for one of us to have had an ancestor who's DNA was longer or shorter since we're talking about the same creature.
Most of these kinds of concerns actually stem from a total misunderstanding of the evolutionary process.
The other thing that I find rather silly (although quite true as you point out) is that people do tend to think that one belief system somehow clashes with the other.
For example you say, "If they are confronted with spirituality, it plants a seed of doubt" Which is utterly silly because there is nothing in spirituality, in general, that conflicts with any scientific knowledge or observations. In fact, many people argue that science somehow 'denounces' spirituality which is to do nothing more than exhibit their own gross ignorance of both science and spirituality.
However, having said all of that, I think that most of the misunderstandings come into play from specific religions and mythologies which DO conflict with scientific knowledge. Often times atheists take the position that sprituality equates to a dogmatic and firm belief in some specific mythology. Of course, in the case of many popular religions this is the case. For example, Chritianity is totally dependent upon the existence and historical behavior of a God named Yahweh, and on the idea that he had a son who walked on water, blah blah blah, not to mention all the other silly prophecies the mythology demands, as well as the existence of a satantic demon.
Once a person has it in their head that spirituality equals a specific religious mythology, then they veiw spirituality in a way that is totally inconsistent with what spirituality actually is.
I think much of the attitudes of modern atheists stems from a very passionate distaste for the Mediterranean mythologies, specifically the Abrahamic traditions built around the mythical God of Yahweh.
The real irony of that whole religion is that Yahweh is actually a name that came from the Hewbew letters YHVH which supposedly represented the name of God. Yet those letters originally represented Earth, Air, Fire, and Water and they came from an earlier version of a mystical and magickal based mythology that was based on a tree of life that later became known as the Kallabah, or Qabalah, or even in the case of Christians, the Cabalah. (using a C for Christ's sake).
As far as I can see all these myths go back to common roots.
Anyway I got off track there a bit, but the point is that most people can't seperate spirituality from religion. They seem them as being one in the same thing which, of course, they aren't.
As Abra said, we didn't evolve from other existing primates; all existing primates (us included) evolved from earlier primates.
