Its common sense, pressure on one pivot point in the middle, there will be long term damage, maybe not noticeable, but the boat will bounce back and fourth like a sea-saw to some extent no matter how well you tie down the bow or stern.
If you don't position the center of gravity properly, yeah you've got a see saw. You just need to make sure the weight is distributed evenly. I don't buy into the "long term damage" unless the boat isn't secured.
I would have thought that hitting a wave badly was far more traumatic to the hull than car topping.
Sailing is going to wear your boat out. Car topping allows you to wear it out in more interesting places!
To any small car owning Laser sailors:
PLEASE don't let the info in this thread put you off attending out-of-town regattas.
It will be fine, and we'd love to see you!