Yes, it is completely optional.

But it's worth mentioning that the phishing mute lists will mainly be used to hide posts from accounts that put dangerous links on their posts (e.g. links to web sites with malware).

So unless you are a careful person that never follows external links, it will probably be worth following at least a phishing mute list. Such lists are not political, they are just aimed at protecting inexperienced users from real criminals.