Are views harmful for performance in PostgreSQL?
The book is wrong. 

Selecting from a view is exactly as fast or slow as running the underlying SQL statement – you can easily check that using explain analyze.

The Postgres optimizer (and the optimizer for many other modern DBMSes) will be able to push down predicates on the view into the actual view statement – provided this is a simple statement (again, this can be verified using explain analyze).

The "bad reputation" regarding performance stems – I think – from when you overuse views and start building views that use views that use views. Very often that results in statements that do too much compared to a statement that was hand-tailored without the views e.g. because some intermediate tables wouldn't be needed. In almost all cases the optimizer is not smart enough to remove those unneeded tables/joins or to push down predicates over multiple levels of views (this is true for other DBMSes as well).