I don't think there is anything wrong with storing passwords unencrypted locally assuming the machine itself has encrypted storage. Malware that retrieves passwords from password manager could get them from an unlocked password manager as well.
Essentially if you have a piece a software with a bug that allows someone to remotely read files from you system, your browser stored passwords are compromised while your passwords stored encrypted are safe-ish depending on how good your passphrase is.
Of course if you have malware that can run arbitrary code on your system you are hosed either way.
A decent password manager will require explicit user approval before disclosing passwords to clients. Regrettably, few do this.