I think there's a difference between (mediated) constructive reflection with the goal of processing an event, and Repetitive Negative Thoughts (RNT) about an event. The latter can of course have long lasting negative effects.

I think it's probably better to reflect on and process a _potentially_ traumatic event, than it is to repress or otherwise force yourself to forget it. But either of those is preferable to dwelling on it and spiraling in negativity.

Perhaps this is just a matter of degree. For really bad trauma (mass casualty, etc) it's probably good to have stronger tools available.