Some day I'm going to have a crippled person hold a door open for me.
OK, are you trying to make him fell better about himself?
No, It's because it's easier than me holding it open for myself
I don't think you are being as nice about this as you should. It is fine to accept a kind gesture from anyone who offers it to you. I think if you are just being plain lazy, then that is rude especially if the other person is struggling with the door.
I just wanted to be different
This isn't being different so much as being rude. Being nice to handicapped people will be more likely to get you what you want.