It is bad technique to rest your forearm on the body? And to do really fast passages is tightening and anchoring your hand bad too?
Carol Kaye gives a detailed description of how to use a pick. Check out tips # 26 & 27 here : https://www.carolkaye.com/www/education/tips1.htm IMO it is not a good idea to rest your forearm on the body of the bass...at all.
It seems to me that Carol's technique requires the player to have the bass AND your arm almost parallel to the ground and having it very high (a bit higher than when sitting - and then thats not comfortable for finger picking). It's because of the part where she tells to keep thumb muscle on the lower string than the one your playing - its impossible for me to do unless I keep things parallel. When standing up I can only mute strings with the muscle below my pinky - my thumb muscle doesn't even reach the strings until I play the G string :/
I don't think is bad technique to rest your forearm on the body... In fact I find very uncomfortable not to, personal preference I suppose. As for fast passages the more relaxed your arm and hand the better. Rememeber to play from your wrist not your arm!!!!