Commenter Malvolio on the Very Nice ACLU Brief in a Student Free Speech Case thread pooh-poohs the ACLU's participation in the case, and writes "let me just say I'll be impressed when the ACLU defends Wal*Mart or Phillip Morris." A quick google search for "ACLU tobacco advertising" reveals that the national ACLU has indeed spoken up against broadcast restrictions on tobacco advertising. So before just assuming that your view of the ACLU is correct, you might want to do a bit of research.

The google search also reveals lots of people criticizing the ACLU for getting contributions from tobacco companies. My guess is that tobacco companies support the ACLU because they like the ACLU's position on commercial advertising generally (which goes back to the late 1970s, in cases such as Bates v. State Bar [attorney advertising] and Linmark Associates v. Willingboro [placing of "For Sale" signs in front of one's home]), and the ACLU's position on commercial advertising naturally leads to protect for commercial advertising of tobacco. But whatever is going on there, the ACLU does indeed defend Philip Morris.