For the sake of argument we can assume the only point of the US immigration regime is to stop baddies from coming in, so yes the goal is "stopping serial killer

For the sake of argument we can assume the only point of the US immigration regime is to stop baddies from coming in, so yes the goal is "stopping serial killers". However, for the reasons I outlined, that doesn't mean we should disband serial killer checkpoints, or refuse to punish people for skipping serial killer checkpoints.