I don't see the point of tag synonyms. I see bond for james-bond and nolan for Christopher-nolan. Wouldn't it make more sense to have a mod approve tags? We can even have people with enough rep do that by retagging. Just a thought.
On a site as small as this, you could have a moderator approve all tags. It would require co-ordination, and a governing tagging 'scheme' but there are only 3 moderators on this beta site. This would start to break down if the number of people grew (more moderators or people with enough reputation).
On a larger site like StackOverflow or Super-User, with many more moderators this co-ordination would be unwieldy and I could see it breaking down.
The tagging mechanism (whilst not ideal) is a way of dealing with tagging without having to have significant co-ordination with other people.
Unfortunately we have to share the same platform with other sites that are significantly larger than we are.
In these examples, we would make james-bond and christopher-nolan the parent tag because it's more descriptive and make bond and nolan a synonym. What this does is it allows people to tag with either one, but end up in the same listing for clarity and cohesiveness.