UNiq: Please read up on U.S. v. Haynes (1968) why a national gun registration is unconstitutional. However, as I stated and you correctly pointed out, it is only mandatory at state level, and only some of them do it. While the state I live in requires registration, I understand why it is opposed on a national level. So no, I do not back a national background check.
However, backgorund checks IS mandatory on a federal level.