For some reason crashing shuttlecraft, and free flight between space and atmo with shuttlecraft and runabouts and such seems... workable.
Crashing capitol ships takes:
A lot of land to crash on.
A lot of different types of damage and damage effects to the ship.
A reason not to, cuz it sounds like a lot of fun, and I don't think we want people randomly crashing their ships at a whim... or for griefing.