Who is worrying about stopping comets?
I would think deflecting would require less effort.
I would think that as well. Much less. Construction workers can push a heavy suspended steel beam into fine position by hand. Same idea.
The atmosphere is not really a defense; it has no effect against anything big enough whose impact would alter the global climate. Sure it prevents small stuff from getting through, but defense here is kinda moot.
The danger is from large objects of course and it's only a matter of time before the cosmic event clock hits midnight again.