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

You said

but say for example, the programmers do a good job of preserving data integrity

The expression you were looking for is, "I'm 100% certain that every programmer and every database administrator will manually preserve data integrity perfectly no matter what application touches this database, no matter how complex the database becomes, from now until the time it's decommissioned."