> somehow this became twisted by the furious mob
There's no mob here. If anything, most people seem unfamiliar with this episode.
> Legally in the US you are guaranteed three months of unpaid leave for getting sick
Except where one qualifies for protection under the ADA [1].
> That's not just not despicable, it's laudable
There are two things here. That Reddit maintained the employee for nearly two years, as you say, is clearly laudable, though this decision predated Pao. My overall view of the situation, and likely this goes for others, is in how it was ultimately handled, where Pao said one thing to the employee then did another, more than once. I can see a situation where this could have been handled openly and candidly, with humanity, but that's not what happened.
Maybe in the end he would have relapsed again, and maybe his doctor would have determined that he was too sick to perform his duties, and maybe firing him for that actually would have been legal (without knowing his ADA status we can't know), but that's quite a few 'ifs'. Not knowing what would have happened, Pao could have addressed the uncertainly in an honest way, but instead she chose to lie to and then fire the employee. I'm not a one man mob, and I respect your difference of opinion, but that to me is despicable.
[1] http://www.cancer.org/treatment/findingandpayingfortreatment...