Sam was an asshole.
It's a magic secret door damned souls have been using for the last million years to duck between two really horrible places... AND HE LEAVES THE MAGIC DOOR WIDE OPEN!!!
What about the next guy?
The next guy is fucked becuase Sam left the magic door wide open and Crowly or one of his minions is going to find it and seal the fucker up.
Is Sam going though all this shit to seal Hell, or to seal the gates, as in the front door to hell. Which means there's still the back door, windows and mouseholes like we saw in this episode... So did Sam want Crowley to lock this mousehole for him so that locking the gates actually means something?