nope, not sending a bday card doesn't make you a bad person, but you are a wonderful, good person for even having the thought cross your mind. it means that you generally are a thoughtful person and its simply that you recognize that sending bday cards are a nice thing to do.
but seriously, don't send it. like those gals say in south pacific, wash that man right outa your hair. and sending him a card does not count as shampoo or conditioner.
i don't know much of your story, but if this guy makes you not feel safe then no way in heck should you send him something that says "i care".
and well, the reason why you can't feel numb is that you're human. if you did feel numb, i think that would be much worse, like that you are hiding your feelings or blocking stuff out. revel in your non numbness cause its good for you to have feelings, no matter what they are.
but yeah, under no circumstance do you send him anything except a plague of locusts, and then only if you get them on sale at tj maxx or something.
__________________
"But I want you to remember, I intend this breast satirically." Susan from Coupling
Nothing, I repeat, nothing is wrong with you. From what I know about your situation (I've been keeping up with your posts), you have every reason to feel what you're feeling I would not send him a card. You are not a bad person if you don't. I think you're a wonderful person, if only because you even considered sending one in the first place (although, we all know you're a wonderful person either way ). After all he's done to you and your son, I'd just say screw it. Please don't send him a card... he doesn't deserve your kindness.
Don't send him a card! He's crazy and you do NOT need to be associated with him in any way right now. It might be hard but just let the day pass. Soon it will be "his bday was last month" and it won't be so bad.