Atheism is a construct, as religion is. Both were developed from empirism.
Things can't be both a construct AND developed from empiricism.
Construct (noun) - an idea or theory containing various conceptual elements, typically one considered to be subjective and not based on empirical evidence.
Empiricism (noun) - the theory that all knowledge is derived from sense-experience.
It's called reductio ad absurdum : it qualifies well in my case since I've gradually reduced the idea of God to nothing.
That's not what that means. I'm starting to think that you don't really know what you're talking about.
Christianism
What is Christianism? Seriously, are you trolling me, bro?
we don't need to know how the universe was created to rule out any divine will or intelligence
I disagree that you can "rule out" divine will or intelligence, but I agree that it is unlikely.
if something exists it must have properties. Since will or intelligence are biological processes and God can't be flesh, thus the universe can't have been created
This sentence is nonsense. How do you define properties? How do you know that will and intelligence are solely biological? Why can't God be flesh? How do these two things imply anything about whether or not the universe was created?
it exists because it has to, ontologically, like some sort of recursive law.
Maybe, but I'd like to see the proof you have for this, since you seem so sure. I'd say there are infinite other possibilities at this point.
Why would you encourage him to stick to Christianity because he hasn't the good arguments
I don't care if he sticks to Christianity or not, as long as he isn't hurting anyone. I do care if his arguments are this bad though. We have enough people making terrible decisions based off of flawed reasoning in this world.
I will go way out of my way to tell people that their decision-making process is flawed, because those decisions may affect me. For instance, if this guy becomes an atheist, and starts telling a bunch of people the reasons that he is an atheist, then people are going to think he is stupid. Since most people are too lazy not to group everyone together, they will come to the conclusion that other atheists believe the same stupid stuff he does. This already affects me on a daily basis.
TL;DR - I don't care what you believe (as long as you aren't hurting anyone), but at least have a good line of reasoning.