I'm going to chime in as a self professed authority on the subject. I'm 27, have been playing bass seriously since I was 13, have been mentioned in Guitar World, play in my church band, high school jazz band, high school orchestra (upright acoustic, finger style and bowing), various other bands, jam bands, etc.
Picking has its perks, but I prefer to play finger style. The tonal advantages of using a pick also have to take the actual strings used into consideration. Try picking on flat wounds and tell me what you think......
As it was stated earlier in the thread, picks can be used to gain certain textures and tonal characteristics that can't be had with fingers. It's up to the musician to decide what is appropriate, and the better musician will make a better decision.
Case in point, John Myung of Dream Theater. He plays finger style 99% of the time. But for a song on their latest cd, which was a little more hardcore and called for a more rigid sound, he elected to use a pick. Simply because the song demanded it.
Then you have Justin Chancellor from Tool, who's songs are more like that one particular dream theater song that demanded picking. He uses a pick usually, and it gives the songs an edgy sound. In this case, I think he does right by using a pick. However, I don't think most people would even tell if he just used finger style, and upped the midrange and treble on his eq.
However, I can't respect someone who solely uses a pick and can't play finger style. To me, bass is a predomantly finger style instrument and using a pick is kind of an after effect of guitarists using picks and then trying to play bass. Maybe im wrong though. Most times, bass sounds better finger style. You get direct touch on the strings, you have more control, can grab and pluck multiple strings without having to sweep across. When I play with a pick, i feel limited and stuck with it. When I drop the pick, I can play any "finger style" that I want.
To me, finger style is the more "intimate choice" for the instrument.