That can't be right, because people flatbase all the time, especially before take-off and after landing. As well as just cruising.
I doubt many people are actually cruising flatbased, thats asking to do what you just experienced.
Taking off flatbased is really only a few seconds of actually flatbasing and hopefully if the park is maintained you won't have any problems. You don't have to takeoff flat either, you can use a low edge angle like cro mentioned. When I land, I try to engage an edge as soon as I gather myself. Landings where I ride are usually sketchy so I wouldn't want to be flatbasing long at all.