Using hobbies is a great way to make friends if you enjoy that hobby. I just think it's a little disingenuous to go to a book club for something other than the book; it feels like going to the gym to just try to chat people up, or really any hobby-related gathering where you don't really care about the hobby. If you're not going to read the book for a book club, it just seems like you might have better luck finding shared hobbies with people at a different kind of club.
Then again, that's just my opinion of what my ideal book club looks like, but that's in no way the "right" way. Social book clubs are probably a great way to get more people to read things they otherwise wouldn't; I just don't get as much out of those kinds of book clubs.