Interesting question @Sage_Ninjistic. In the US there was this hoax in 1950’s. A guy (I don’t remember his name) who declared that he was able to increase the sale of coca cola dramatically and popcorns I think by the people watching a movie through visual subliminals. This “experiment” created some kind of frenzy, panic in the society to the point that subliminals were banned from commercials in the US. But, in fact, the guy recognized that he did a hoax, just a marketing ploy. Then there was the so called backmasking satanic messages in songs of certain popular singers. Nothing has been proven. Then in the 1980s-90s many people in the self-development area started to create subliminal tapes for self esteem, confidence etc. Psychologists started to study “scientifically” these tapes and declared they are a waste of money, placebo effect only. So the pioneers in the subliminal sector continued their experiments but more underground, using other vocabulary like priming the subconscious. All these things on subliminal happened mostly in the US and UK, english speaking countries in general
For us, in Europe, in France for example, this sector is mostly unknowned. Very few French have ventured in this area and those who did had training from Canada or the US.
Why do I say all these things ? in France it is not a taboo, it is just ignorance and/or curiosity 
Alternative medicine is gaining ground for the best and for the worst. Sophrologie, yoga relaxation and hypnosis are becoming mainstream and fashionable . But subliminal, still nothing.
I have talked about subliminal with some members of my family and friends: their reactions were classical : what the hell ! you listen to the ocean and you will become confident overnight, uh, another marketing gimmick from the US ! But I have been able to convert some members of my family, my wife being the first and foremost 
The problem with those open minded people is that they are not consistent. They will listen one day and then forget for a week. Or I have to reminder about it once in a while my wife. I consider myself a “lifestyle” subliminal listener. I can’t imagine a day without listening to a subliminal.
Other members of the family, I will never talked to them about the subliminal, I know already their reactions already yoga is esoteric for them 
So I just choose to whom I talked to for this strange practice of listening to white noise, river stream or ocean But I can’t say that it is a taboo
