As a physicist, I do not endorse Creationism or Intelligent Design. Short of that, while studying physical measurements of cosmic events and the corresponding mathematical models of the origins of the universe and all that lies within it I have been overwhelmed by the ultimate imponderability of it all. That is to say, if the human race survives a billion years, human beings or their evolved descendants will never comprehend the universe, especially its origins.
Bear with me while I establish a few premises for the relevance of this to agnosticism versus atheism.
Physical measurements and mathematical models of the universe to date indicate that the universe is eleven-dimensional--counting time. A two-dimensional creature living on a two-dimensional surface could not comprehend a sphere or a cube by the two-dimensional projection of the three-dimensional cube or sphere onto the two-dimensional surface on which he lives. Similarly, we cannot comprehend our eleven-dimensional universe from the four-dimensional (counting time) projection of our eleven-dimensional universe that we experience in our four-dimensional world.
To further complicate our attempts to fathom our universe, physicists specializing in cosmology have made some physical measurements and constructed mathematical models of the universe and its particles and cosmic bodies that show that "ordinary" matter and energy with which we are familiar makes up only 4 percent of our universe. "Dark matter" which does not interact with light or other electromagnetic energy, and so cannot be seen, but which can be detected by its gravitational actions, accounts for 22 percent of our universe. The remaining 74 percent of our universe is made up of "dark energy", which is poorly understood, but which is driving the accelerating expansion of our universe.
The remaining complication of our attempts to fathom our universe lies in uncertainties about its origin. Cosmologists are continually gathering new data, re-examining old data, and building and revising mathematical models to evaluate several concepts of the origin of our universe. Whichever concept ultimately stands the test of measurement and mathematical modeling, the candidates for the origin of our universe must reduce to two categories: (1) our universe sprang out of empty space, from "nothing" at the instant of the "Big Bang"; (2) our universe has always existed (Since our current universe is rapidly expanding from the "Big Bang", this draws on theories that allow for events (time) in another dimension before the "Big Bang"). If the "Big Bang" model is wrong, then the universe still either sprang from nothing or has always existed. Either way, time had a beginning, or it did not. Either way, it is imponderable.
Given these imponderables--that the world as we know it is a four-dimensional projection of an eleven-dimensional universe, that "ordinary" matter and energy make up only 4 percent of the universe while the rest of the universe is "dark matter" and "dark energy", and time is incomprehensible whether it had a beginning or did not have a beginning, it is difficult to speak of logic, but one can say that there is no basis for drawing any conclusions about the "cause" or lack of "cause" of the universe. We simply do not know, and mankind will never know--the position of the agnostic. The position of atheists is not warranted, because they are drawing a conclusion about imponderables. The agnostic position is warranted because it does not draw a conclusion because of the imponderables.