- they're going to do their evil thing anyway, may as well show up and intentionally do it marginally worse
- they're going to pay someone large sums of money, may as well be me
- I increasingly believe this whole industry is net evil overall, and large sums of money mean I can leave it sooner
- also, it was their VR thing, and if it was a VR thing at literally any other company I would be excited about that because VR is at least conceptually cool
These are not particularly good arguments, and that's why I don't work there now. But statistically, I can imagine a few people who we would otherwise categorize as non-evil actually convince themselves with arguments like these, and when you're casting as wide a net as Facebook does, a few is all you need.
Here's the thing: anyone who is in IT, especially programming; is going to be well-aware of the...I don't want to say 'evil', but I will at least say questionably ethical nature of Facebook's workings.
Anyone working there had to compromise some level of ethics for the profit they acquire from it.