There are plenty of reasons, beyond ideological ones, not to want to work there. I don’t think I have any ideological objections to Facebook, but the product itself doesn’t interest me and I’m not a user.
I don't work at FB but I'm sure for a product of that scale even if you don't use or care about the product itself, there may be interesting projects for you to work on.
I also don't think I'd care to work on FB the product, but I'm sure it'd be interesting to get to use Haskell to fight spam and work with Simon Marlow. They also use OCaml for some compiler stuff that I'm sure would be interesting.
I agree and am not sure why you think I thought otherwise.
The person I was replying to said "I don't think I have any ideological objections to Facebook" which I assumed to mean they don't see any moral problems with Facebook.
I was merely disagreeing with the idea that someone's lack of interest in the exterior facing product implies there are no interesting projects for that person in the entire company.
It's definitely possible, but they'd probably be working at another top tech company or finance company (think Citadel, Google, Jane Street) or starting their own company instead.