Who forbids it?
In occultism, "left hand path" means black magic. So it would be the "right hand path" followers who forbid practice vamachara.
Basically, by definition it is about breaching Hindu societal taboos, unless I am vastly misunderstanding this brief summary.
https://en.wikipedia.org/wiki/Left-hand_path_and_right-hand_...
It isn't obvious that asanas, breathing exercises, mantras and visualisation are somehow breaching any taboos of any society that I know of ;)
Why do we consider those seriously while making fun of LaVey's rituals?