Stripe's fraud protection is HILARIOUSLY bad. I'm convinced they don't care about chargebacks; in fact, to get their fee for a chargeback, they need a $500 order.
I'm working on a side project using Stripe and at least most comments on the internet are saying that the fraud prevention provided by Stripe is rather weak. Adding additional providers like SiftScience looks like a good idea.
Full Disclosure: Not based on first hand experience, as the project is not launched yet.
They don't eat the loss; the card network does.