Atheists, tell me, a Roman Catholic: why should I become an atheist?

[Kernel Sohcahtoa]

First off, welcome to AF, Balaco.  IMO, I do not think you should become anything; what you become ultimately rests with you.

Atheists, why do you reject the idea of God, and why should I? I know that your answers will include "there's no evidence" and all that, but please try to explain

I do not feel the need to reject anything.  From my vantage point, it seems premature and somewhat shortsighted for me to limit myself to the current worldviews/theories of perceiving and understanding our reality; perhaps another sentient life-form would view our concepts of theism and science to be an archaic means of understanding reality: there could be so many fascinating and creative ways of understanding and perceiving our reality that are just waiting to be discovered; yet, their discovery may be inhibited by the human tendency to make our observations fit with existing mindsets/beliefs rather than modifying our mindsets/beliefs to fit with our observations. 

Now, I realize that this answer in not a very precise one, and for that, I apologize, sir. Hence, my aim is to share my passion for curiosity and imagination, two traits that I highly value, and which help me choose my own path and create my own meaning in this world.