They would feel much better about themselves if they used their knowledge of the cult to help other people get out of it and warn others about the dangers of it.
As one who has never been a Witness, I can't really speak with too much conviction concerning exactly how most ex-JW's feel about their past. I somewhat feel that whether people ever were JW's or not, many people don't experience a lot of the things in their lives that they would've liked to. The WT might be a very legitimate source of blame in that it's very likely many people may have led a very different lifestyle that may or may not have been better, while others may be somewhat different in that they might blame the WT for things of their own doing that not even the WT had anything or very little to do with.
I think that people should find a way at some point to do what they can do now and play catch-up, if possible. I feel there is a genuine need to be upset with a situation that may have cost a person a lot over an extended amount of time, but I think if people are able to keep advancing in their own lives away from the org, they will be a lot happier as further time goes by.