Probably worth noting that the taking a knee gesture for the 6 Nations isn't aligned to support for BLM but rather the statement "Racism is not acceptable in rugby, in sport or the world we live in". I guess some players (and others) see that as a tacit endorsement of BLM given the gesture's use originated from BLM support and Colin Kaepernick.
Would be interesting to see if the above were more clearly stated whether it changed players' choices. I reckon the unions have got it right though, it's got to be down to the players to make their own decision about whether or not to do it.
Despite its good intentions I think the gesture is in danger of becoming counterproductive. The longer it's used the more its impact is diminished and the more we'll see weird squabbles over what it means to do it, not do it, what exactly it's purpose is, how long does it continue, etc.
Different sporting authorities and other organisations can try and fool us all they like that their taking the knee is not aligned to BLM.
Everyone knows that it is and very many do not like it and will not be bullied into it.