The opposite of faith is not atheism just as the opposite of love is not hate.
Take this example of hate as opposed to love; In this awful scene, the character played by Glen Close is spilling vile hatred on her father. (It is disturbing. If you don’t want to watch it simply know this – she went to see him on his death bed to tell him she hates him and will never forgive him.)
Even though she obviously hates him she is still in relationship with him. It is a sick relationship, but she is still connected to this man she despises. She feels a need to communicate. What happened in the past matters to her. What he thinks and feels matters to her. And when she leaves the room he still has control over (will still have control over her after he dies!) It may be a sick relationship, but it is a relationship. And though we would hardly call any aspect of this love, it is not the opposite of it yet.
The true opposite of love is indifference. With indifference there is no relationship, there is no caring how the other person feels or thinks. There is no control over the other person (positive or negative) because there is no type of connection at all. It is the story of the rich man and Lazarus.
In like manner, atheism is not the opposite of faith. (There are many types of atheism so this is speaking rather broadly.) There are atheists that spend their energy fighting notions of God, which puts them in relationship with Him unwittingly. There are atheists who build their moral construct on viewing the world by observing it and seeing how it seems to operate at its best, which brings us to Natural Law, which ipso facto brings order and intelligence to the universe which brings us to God. There are atheists who rely solely on science, which often leads him to faith. Let us suppose that he relies on the theory of the Big Bang as the birth of the universe (put forth by a Catholic priest by the way.) It still explains nothing. What caused the big bang? Why should there be energy as opposed to not? Why should there be matter as opposed to not? In the end (or in the beginning) the whole thing is established on faith of things that are completely un-provable.
The relationship with (or to) God may not be a healthy one (from a Christian perspective) and the faith in SOMETHING that gives order or was a first cause may be materialistic in nature but it is still faith.
The true opposite of faith is thinking that the world and all that it is in it is a complete fluke of nature. Life has no meaning. The existence of the cosmos has no meaning. This whole conversation would ultimately have no point. Truth is non-existent. There is nothing cognitive outside of ourselves (and even that may be an illusion) and when humanity passes away it won’t matter. The universe will continue to go on and there will be nothing to mourn the passing of man or all of his works and thoughts. It wouldn’t mean any more if we had just been rocks. So eat, drink, and be merry for tomorrow we die.
But let one tiny ray of order, meaning, or the holding of something that cannot be proven, then there is a relationship with something that most people call God no matter how flimsy. Catholics may not think it a healthy relationship. But it is one. And therefore not the opposite of faith.