The ESRB rating is a voluntary rating system that was created by the gaming industry to help provide guidence for people when purchasing games.
The quesiton is would you purchase a US-released game that didn't have an ESRB rating for one of your current consoles before finding out why it wasn't rated? Why or why not?
I didn't leave a "maybe" option open... for the sake of argument, it is a game that you are interested in at a good price. Do you take it, or leave it?