Do you absolutely need foreign keys in a database?

Question

I was wondering how useful foreign keys really are in a database. Essentially, if the developers know what keys the different tables depend on, they can write the queries just

Answer 1

I think that assuming that programmers will always preserve data integrity is a risky assumption.

There's no reason why you wouldn't create foreign keys, and being able to guarantee integrity instead of just hoping for integrity is reason enough.