Ahh but it was an Earth ship. Marcus would have been a bit stupid if he designed a ship that would get blasted by Earth Defense?
From what I saw, he WAS pretty stupid...
Are you suggesting that Earth defences should be incapable of scanning a crashing earth ship? That they would be unable to detect the single life form on board (don't get me wrong, personally, I think they should NOT be able to detect anybody who isn't wearing a communicator, belt monitor, or injected with a beacon but that genie got out of the bottle decades ago)? That allowing a ship to crash into a city , most likely killing citzens and everybody on board is preferable to just killing everybody on board before it hits or better yet, using surface to air shields or surface to air tractor beams?