A while ago, I encountered a demotivational poster about atheism. I didn't find it back, though.
It said something like: "Do you believe in quarks? You didn't see them or prove their existence. So that's faith."
At first, I wanted to make a rebuttal. But, even with eight years of physics education behind me, I couldn't. I have seen atoms and electrons. I've measured radiation. But the strong force is really difficult and, as I didn't choose to specialize in it, I don't know how it works. Well, I know the basics, but not enough to prove, even to myself, that a quark exists.
So I had to ask myself the question: why do I believe in quarks, and not in unicorns? You can call it faith, but to get rid of the religious overlay, I'd choose to call it trust. I believe in quarks because some people have told me about them and I trust those people. Now, of course, why do I trust the quark people and not the unicorn people?
Because the quark people, the scientists, have told me many more things I COULD check and measure. I've spent my whole life being interested in science and measuring things. Because the scientists are the ones who encouraged me to observe and pose hypotheses and experiment and make conclusions. I can't test everything myself, because I don't have the time and money for that. So I do understand the electromagnetic and the weak force in terms of particles like electrons and photons and neutrinos. And when they say "the strong force is just like that, but with quarks and gluons", I tend to believe them. They fit with the other particles. To be really precise: I believe the Standard Model is a good model to predict particle behaviour.
The unicorn people never showed me unicorns, dragons, fairies, ghosts or anything else that would help me believe in unicorns. Worse, they tend to say you have to have faith, that it is a virtue to believe without any evidence.
A last thing. You are free to believe in unicorns. I won't hinder you. BUT.
1) If you want ME to believe too, you know what you have to do. Evidence, please. No emotional blackmailing.
2) If some idiot insults the unicorn, you don't start killing random people who have nothing to do with it. Wear a T-shirt with "Proud Unicornist" on it. Insult the quark. But don't riot and destroy and kill because of an idiot.