Why do people dwell on Obama's "lack of blackness"?

You are 100% right! The people who were against Obama in the beginning now need to accept the fact that he is president so they are making themselves feel a little better by saying "Well...he is only half black, his mom is white!" but I guarantee you that if Barack Obama was a regular black/white guy and a conservative mother had her daughter bring him home, he would be labeled just a black man real quick!