iamleppert, are you me? I went through literally the exact same situation (same problem with the manager, same outcome, etc.), though instead of quitting I finished the pip and switched to a new team (I was already on another team by the second or third day of the pip as I was taking it to HR, which doesn't always work out - it did in this case).
New team thought it was absolutely ridiculous I was on it, as did many members of the original team. I finished the pip just fine. I work at Large Transportation Company. Same shit over here.
Once I was working with a manager that loved the fact I'm gay, I do great work, stress levels are down (or at least, the stress incurred is the 'fun' kind of stress), etc.
I do agree the review process is ridiculous - I've never been in a company where they had them prior to this. We were told to choose 2-5 coworkers that were really involved in our day to days within the review period (6 months), and after doing so my manager went in and added the rest of the team (including coworkers I barely saw that I had one or two interactions with over the course of months), including other coworkers that had made very brash comments about my boyfriend/age or about gays in general.
Manager used that shitty feedback from three out of the nine total employees that reviewed me (that otherwise gave pretty glowing reviews) to initiate the pip.
There was a whole bunch of other BS with the situation - e.g. a manager and another coworker joking about satanic rituals against us in our team HipChat room - that I really don't feel like going into detail about that just added insult to injury.
What's worse, there has been no investigation into the matter much past asking the offending manager to "talk about things". Oh well.