Can a full fluid flush be dangerous for the transmission?

A simple drain and refill should not put any pressure on particles inside the transmission. Any particles that are stuck somewhere should not come loose by draining it. Many places will disconnect the trans fluid cooler lines and drain/refill using the transmission's own oil pump. They put one line in fresh fluid and the other drains to an empty container until the fluid comes out clean. This way the transmission does not see excessive fluid pressure or more pressure than it normally would experience. "Flush" is not always a clear term in the industry so it's good to ask what they do.

Any transmission flush is better than no fluid change at all, Most transmission failures are caused by running on burnt fluid, Make sure to change the filter also.

My car dealer recommended a transmission flush and replace the filter for my 2000 Blazer, which I did. A week or so later when stopping, the transmission shifted violently into first gear. Took it back to the dealer, result, $1000.00 to replace the valve body. There was no problem before. I'll never, never, never, ever flush a transmission again!!!