I went and read more into Shar's cult , and it sounds like SH shouldn't be sharing her worship with you unless she was trying to recruit you. Also, the requirement to become a cleric is indeed pretty terrible, so I better understand where some people's strong feelings are coming from. It reminds me of Mephala or Boethiah from Elder Scrolls.
Based on all the inherent secrecy, it doesn't seem like most people in game would know the Sharran requirements and symbols though (at least without a moderately difficult religion check).
Okay, seems like we can find at least some common ground, which I appreciate.
I would disagree, though, about average FR people's extent of knowledge about Shar. Firstly, I don't think custom Tav is or should be considered average. And furthermore, Shar's monstrocity in the Realms is so enormous that one would have to literally be living under a rock to not know basic things about her, such as her symbols and the extent of her evilness. I mean, it's only been a short few years since she waged a horribly destructive war across a large swath of the Realms in an ettempt to further her nihilism.