A few things to consider when asking about one's faith in humanity.
To begin with, "faith" is belief without evidence. So by definition, if you "have faith in humanity" than that means you simply believe in humanity and should not feel the need to back that up. Now, the atheist community has verified that a major pratfall to faith (in anything, doesn't have to be religion) is that it fails when one introduces "reason" into the mix. This to be remember as we progress further into the discussion.
Now, my own beliefs on humanity one might wonder? Its simple really. Any given human is one of two things: their either an outright monster or an outright dipshit. This I can back up too. There have been studies done over the years that have proven that humans are highly conformist people whom have tunnel vision and are cowards that follow the leader with blind faith so they don't die or worse. Garbage in the media sells for a reason, and studies show that we don't like nice people, and that we, knowingly or not, discrimate against others for the stupidest reasons.
That's just the dipshit aspect covered. Nevermind the fact that our world leaders, politicians, business folk, barons, and bureaucrats benifit from the vast majority of us living in misery, despair, poverty, and undignitly and therefore the vary people with the power (the aforementioned) have no insentive to change anything.
Now, I know you might be thinking that this means more than I simply lost faith in the human race: I'm an outright misanthrope. You would be right: by definition this would make me a misanthrope.
Now, someone has already mentioned the "If you lost faith in humanity you have to have lost faith in yourself." Now, here's the deal. I'm not a powerful person. I'm not a strong person, neither of body or mind. I'm not a particularly pretty person. I'm a deadbeat living in their parents' house that is destined to die a pennyless, forgotten nobody. I'm refuse just like the rest of you out there. Oh, and I'm also likely not a particularly nice person.
You wouldn't have to look any further then your favourite news feed to know just how horrible our world is, and how it amazes me that to be happy in it you have stupify yourself by playing stupid games and being chemically impaired.
To answer subject_87's question of what it would take to restore my faith in humanity, I would like to point to the second paragraph and stat that by definition I can't have faith in humanity because I've already concluded with reason that humanity is scum and reason trumps faith, period. However, you're likely more intereted in what it would take for someone to like humanity and look at the race more favourably and optimistically. All you would need to do is, well, prove me wrong.