Not to be defensive here, but just because I refer to learning to play with your fingers as 'proper' does not necessarily mean that I consider anything else 'improper'.
My point is this; Slang is not necessarily 'improper' when it comes to being effective, but speaking using correct grammar and sentence structure is 'proper'. Both are perfectly fine ways to communicate, but I feel it is important to learn how to speak correctly before you choose to branch out and explore more colorful ways of communicating. Imagine if you never learned that "ain't" in not necessarily the most appropriate word and you had a very important job interview where your ability to speak properly would be considered...
The same concept applies in many disciplines, including bass playing. In my opinion, there are fundamental skills that a person who is just starting out should learn. Hell, they don't HAVE to do anything and no matter what direction they choose - pick, fingers, toes, whatever, they could make an amazing contribution to the musical world as did McCartney. But when a beginning bass player asks the question, "To pick or not to pick?" I am always going to say "Start with your fingers, then experiment with other techniques and don't rule out anything" Music is not only a language, it is an art and should not be restricted by opressive rules.
Just my opinion.