For me, all this parenting "stuff" is about choice. As parents we have a lot more choices than our parents did in the '60s and '70s (they didn't even have car seats then!). You can choose between a $120 stroller, an $800 one or even a $2000 one...or you can borrow one or spend $40 on a used one.
It's the same regarding baby sign language. You can choose to teach your baby sign language or not. You can choose a free resource that you can get from your library or from the internet. You can buy a book, flashcards or a
If you choose to teach your baby sign language which of the above you choose depends on what kind of learner you are. Maybe you are a book learner and can get it all from a book. Maybe you are a visual learner and want to see an instructor make the signs. Everyone's different.
The great thing about taking classes (which may be free classes at your library or paid classes at another community site) is that you can get feedback immediately about how you are signing. Your instructor, if he or she has a background in sign language, can give you immediate feedback and corrections regarding your signs.
As well, I've had parents in my classes who just love the social aspect of getting out with other adults who have babies the same age. There have even been instances in classes that I recognized that a baby is signing their first sign and I help a parent see that as well!
Using baby sign language with babies and toddlers is a good thing and it should be a choice that is given to parents. Using baby sign language is a parenting tool and it's a great option for those who choose it.