No, it's not. It's a forum to discuss multiple topics including religion.
It can be the only reason why you are posting here on a so called religious forum
You suffer from a poverty of imagination if that's all you can conceive, but that's fine. It's not important that you understand what motivates critical thinkers.
your defensive atheistic views
Do the atheists you are debating seem defensive or insecure to you? Do I?
It is a religion because it is based on faith in science
You have a lot to learn about both religion and faith. Atheism is less of a religion than theism, which also isn't a religion. And there is no faith in science. You only need to look at its stellar success to recognize that its foundational precepts and its testable inductions are correct.
you have no facts to dispute the existence of God.
Did you mean gods? I would agree with that. There is no way to rule out the deist god, for example.
But if by "God" you mean the Abrahamic god, that god has been ruled out empirically. One look around and we can see that no tri-omni god exists, and if life on earth was intelligently designed, it would have to be by a deceptive, superhuman presence that planted evidence in the earth and the genomes of living things to make it appear otherwise, one that need not be supernatural. That couldn't be the god of Abraham, and if the deceiver were a supernatural entity rather than advanced extraterrestrials and there is an afterlife, that's not an afterlife to look forward to.
Also, I have no use for facts to rule out your god or any other. I already wouldn't believe in your god without it being ruled out, and believers aren't moved by sound, evidenced argument, so what use would such facts be to either of us?
Can you give a stable, rational reason why you should challenge the existence of God
I just did, assuming "God" is Yahweh to you. But I've also given you a reason why no such thing is needed. All the theist has is an unfalsifiable (insufficiently evidenced) claim, which can be disregarded without rebuttal and filed under, "The other guy's opinion" along with his favorite Beatle and favorite flavor of ice cream if he's told you those as well.