I work in IT security for a large financial firm. We've spent a good amount of time convincing the development community and the business that security is THEIR responsibility and have built processes to reinforce this (i.e. if folks want to do truly risky things, we can make them go get signoff from senior management). With check in place, I feel we take the approach of "doctors" for applications/architectures.
Dev team is building a new architecture to trade with an exchange? They ask us to review their architecture before they build (sort of like a checkup before going to climb a very dangerous Mt. Everest).
User accidentally e-mails confidential information to the wrong counterparty? We help them work with legal to get things cleared up, give training on appropriate data handling and add client controls to their outlook. (I.e. tell a kid not to run with scissors, take away the scissors and put band aids on the wounds)
In this light, I feel I'm proactively helping folks and treating those who have run intro trouble. Security folks are able to have a broad view of the solutions available to common problems (even outside of security) and teams get value out of this. I've even had folks say (and mean) thanks after meetings that involved them totally re-architecting their application. With the right approach, you can be more than a roadblock...