Putting someone on your personal blacklist will, by default, only affect your personal experience using the web sites. So it's far from a "loaded gun".

In practice, the existing mute list is more powerful (because when you mute someone, you no longer see their posts, whereas when you put them on your blacklist, you just see a warning beside their name).

The only time someone's blacklist becomes influential is if many people decide to use that blacklist for their own account.