This is a pretty tough definition of correct, though. Without foreign key constraints you'll have a really tough time dealing with concurrency artifacts without raising your isolation levels, which generally brings larger performance concerns.
My experience is that if you have a moderate amount of foreign keys, a lot of DBMS (not Postgres) will refuse the `ON DELETE CASCADE` (in the diamond case), and you have to do it "manually" anyway (from your query builder).
I think it because a significant fraction of my career has been spent fixing db-concurrency-related mistakes for people once they hit scale :-).
I’m not talking about using cascade - this applies perfectly well to use of on delete restrict. FKs are more or less the only standard way to reliably keep relationships between tables correct without raising up the isolation level (at least, in most dbs) or doing explicit locking schemes that would be slower than the implicit locking that foreign keys perform.
This is a pretty tough definition of correct, though. Without foreign key constraints you'll have a really tough time dealing with concurrency artifacts without raising your isolation levels, which generally brings larger performance concerns.