Pheromones and sweat odors are entirely different things biologically speaking. :)
Maybe the word "human pheromones" simply has too much baggage at this point after being attached to so much "woo woo" but studies on MHC molecules in body odor and the influence they appear to have in sexual mate selection often (perhaps incorrectly) uses the word pheromone interchangeably with this phenomenon.
All the more reason for us 'rationals' and educated people to not propagate the error ;)
It's simply not a 'universal' taboo. There is tons of evidence from various first nations in the Americas where sibling parings occurred. Also European nobility practiced sibling marriage quite a bit. In smaller human groupings, biological reproductive imperatives required humans to strike a balance between outbreeding and inbreeding. When inbreeding, siblings were simply part of the game. There are genetic price to pay for too much outbreeding can be as costly as too much inbreeding.
American first nations who practiced agriculture also had sibling pairings -- up until white clergy imposed Christian dogmas upon then. You were discussing 'instincts'. The point I was driving at, via biological imperatives, was that the main factor for this taboo is not 'instinct' but social engineering. This 'moral' concept, is a human construct.
As far as today goes... one must not only look at the 'public opinion. One must assess our 'instincts' with our actual behaviours, no matter how dislikable they are to you. The fact is that there is an awful lot of sibling incest going on in our modern society... it is frowned upon, but it is common nonetheless.
As with many aspects of 'morality', what we say and what we do are surprisingly different.
So when a woman says I'm like a brother to her does that mean I still have a chance?
There's always hope