i always find fault with people who find fault with how someone plays... techniques are guidelines and not laws of guitar playing.

with that said, it's still a good idea to learn both with a pick and without a pick... personally, i rarely ever play with a pick. i use my index finger as the pick - to the great dismay of my index finger. in recording and song situations you might find it hard to get the sound you want without using a pick. as someone said earlier, you get different tones with different plectrums.

i'd say keep practicing with a pick but also do what is comfortable to you and what gets the tone that you want.