To a point. If you make it too long, though, you encourage people to try to "beat" the light, and hence they speed up like maniacs when they see it. That's not going to save any lives.
This has been documented. Longer yellows save lives. Unfortunately, they decrease revenue. Hence shorter yellows and red light cameras.
I've heard these allegations for some time, and I seriously doubt this is the case. The appropriate yellow interval at a stoplight is dictated by the speed of the roadway and the distance at which the signal head can be seen by approaching motorists. An engineer who attempts to reduce the yellow interval below this "design" threshold is designing an unsafe traffic control device and is therefore exposing himself to disciplinary action from his state licensing review board.
I've made this offer on FreeRepublic before: I will represent anyone who believes they have been victimized by a "red-light camera" system in which the yellow interval has been reduced to a substandard level. I get 50% of whatever civil damages you net out after your legal fees are paid, with a special 10% bonus to be paid once the engineer's license to practice is suspended.