I wouldn't have any problems with a C-172 or PA-28 door coming open and indeed during my distant training was taught to open a door during PFLs in case the subsequent arrival distorted the frame and trapped the occupants.
What I am not so sure about though is the DA-20 Katana I am flying at the moment. Its hinged in a way that it lifts and travels backwards and I don't know what the consequences might be of it coming unlatched at 120 kts. Certainly opening it on the ramp on a windy day meant it opened very briskly and needed to be held carefully to avoid it banging back onto the stops.
Any experiences with Diamonds ?