If nothing else, the song is a good example of how someone can become a folk hero, by being immortalised in song. Folk songs celebrate the bad, the weak, the unfaithful, the failures and the downright unpleasant as well. I tend to go along with Sapper's view here - although that does not affect the merits of the song in any way.
The lifting of a few used notes is not enough to give me a bad hair day - even bearing in mind that ultimately, I have to pay for that piece of work too... Sapper rightly reminds us of Jack Mills, the train driver. It is also worth bearing in mind that the criminal careers of the participants did not all end when their sentences were up. Both Roy James and Bruce Reynolds, I believe, notched up further convictions. Among other further offences was a major drug smuggling racket.
For the most part, Ronnie Biggs has led a miserable, fugitive life. He is now dying. We can enjoy the pictures of him sunning his arse on Brazilian beaches in the seventies, but his first wife and family may not be taking out those photo snaps so often. Buster Edwards committed suicide. Other members of the gang have been in and out of prison.
If I ever go in for crime as a career, I'll do it the way Woody Guthrie recommends it - with a fountain pen. The "Great" train robbers were really pretty small men.