The real bummer is not that you have to manually refresh them, it's that refreshing them involves refreshing the entire view. If you could pick and choose what gets refreshed, you might just sometimes have a stale cache here and there while parts of it get updated. But refreshing a materialized view that is basically just not small or potentially slightly interesting runs the risk of blowing your write instance up.

For this reason I would strongly advise, in the spirit of https://wiki.postgresql.org/wiki/Don't_Do_This, that you Don't Do Materialized Views.

Sure, Differential/Timely Dataflow exist and they're very interesting; I have not gotten to build a database system with them and the systems that provide them in a usable format to end users (e.g. Materialize) are too non-boring for me to want to deploy in a production app.