My favorite thing as a trained musician in other disciplines about not having a teacher on the violin is that I can address my needs myself as they arise. I am constantly learning to listen to my body, to my fingers, and to my instincts. No one is rushing me. No one is making me doubt myself. No one is pushing me to do things at their behest. Each decision I make in my training is a personal accomplishment I can take ownership of and responsibility for.
Double stopping is viewed broadly as a pretty advanced technique. It is treated as a “next-step” to be taken once a violinist has mastered playing a single line in tune across multiple positions and strings. Isn't it fair to say it would be an ideal accomplishment to be able to play single-line passages and pieces well before incorporating double stopping, which would overcomplicate your accuracies?
These views are fatally flawed in not recognizing that playing an instrument is a gestalt. Limiting oneself to overly-isolated studies allows the fingers to find coordinations that may work for the limited scope of material at-hand but may be practicing deficiency as pertains to the overall goals of the instrument.
The known should always be an indicator of other unknown factors. In double stopping, the known is that it imposes much stricter requirements on the player for accurate intonation. Double stopping is merciless in this. If one of the two notes is a hair off, you are immediately assaulted by beats in the sound.
The unknown is what is most dangerous. What deficiencies are being retained in the finger coordinations by not working with double stopping? What minute graduations in finger arch and the frame of the hand are being unrefined by never fingering more than one string at once? What lack of flexibility and muscular static are being strengthened by never going beyond one finger at a time? I don't know. And I refuse to be defeated by the unknown. I look forward to digging into Ševčík Opus 9!!!!!