Cynicism is a filter of reality and not always correct in judgment. I would consider myself somewhat of a misanthropist, but I hold no vendetta against humanity. I see it for all it's ails and I accept it, and if I want anything changed, then it's up to me to do something about it, rather than sit and be negative about it. Afterall, you could very well put yourself in an environment that countered your cynicism, and what then?
I take life as it comes. I prefer to take unnecessary value judgments out of the equation when it comes to how I judge reality. I don't like to hold onto ideas and have them "become me". I prefer to continually challenge them and critique their origin.
I highly doubt any person is wholly negative or wholly positive. That black and white view of the world is ultimately misguided.
I do think infps' with a largely positive upbringing go through a period of a "loss of innocence" where through experience or information, the positive and innocent veil finally comes off and the full weight of existence dawns on them. That probably entrenches itself the minute the infp engages in full time work, or goes off to live on their own. The infp can either adapt to this new paradigm, or they become bitter by it (probably because their expectations for life were never met).
I see no reason to be bitter, when I compare what the past has been like (where there were less opportunities for entrepreneurship etc) and see visions of the future, look at the options, asses how much hard work i'm willing to do, looking outside of the box and seeing the possibilities. I see a reason to be prepared for external work and internal shifts, not to be bitter. If I want anything in this life, I have to work for it. I aint entitled to squat; I'm not entitled to happiness, love, security etc. None of that is a given. I'm not going to blame anyone for that. That is the reality of life, and I will "receive" what I am willing to work for and for what chance (the situation out of my control) provides.
Life is just a roll of the dice. Taking responsibility and acknowledging what you cannot control, is freedom. Not seeing it in a certain way as a defense mechanism.