Don't be too hard on ElectricPaladin, his heart is made of cogs that are three sizes too small.
I was made to defend mankind from all its foes, but I was never designed to love.
What happens when mankind's foes try to destroy us by removing emotion?
When that happens, only Scattercat can save you.
Because I'm... too emotional? Because I'm so annoying that no alien power will be able to stop people from sighing about it, and thus that scrap of emotion will be retained forever, and we will defeat our enemies with the power of mild irritation?
Anyhoo, I was okay with this story, although I'd rather have seen the birthday party scene first, to really create some suspense about what's going on, followed by the boss at the party, where the nature of the disease becomes readily apparent (and which would create an "ooooh, so that's what was going on!" reaction to my newly place first scene), and follow THAT with the framing device of Santa's captain's log entries. As it was, the birthday scene, while fun, felt kind of redundant; we'd already had the source and the nature of the "disease" explained to us. Not to mention that the birthday scene involved an honest, sincere attempt to give someone something nice for no reason other than to be generous, yet Santa's heart remains unmoved until... another child makes a similar honest attempt to give something out of generosity, except this time only after their parents nagged them (as opposed to the birthday kid, whose parents tried to convince him NOT to give the cards). It made Santa's abrupt turnaround feel completely unjustified, whereas if we'd just seen the boss-at-the-party scene and had it implied that this was by far the more common scenario, his unbroken cynicism would make more sense.
I do gotta agree that the flood of Santa Claus stories around this time of year (mostly "edgy" and "subversive" reinterpretations) gets a little wearing, and I was raised in the religion in question. (Electric Paladin, I happen to know, was not, and thus his reaction to Santa Claus is perhaps more understandable.)