Sure, it might happen, in only the most extreme cases, but it's certainly not the norm, and it makes people who try to take their faith seriously - even if, yes, LaVeyan Satanism is simply libertarian humanism combined with, quite honestly, a fairly weak system of Ceremonial Magick, if it makes them happy, let them do it.
I don't agree with Catholicism, either, but I'm not running around saying all priests rape little boys, even though there is far more evidence of that, than actual human sacrifice in Satanism.
The latter do tend towards being the awfully nice people you've been describing, who are always making sure that everyone is fine in the mosh pit.
The former, however, can conversely tend towards the type of person who is far too enthusiastic about the technical details of the blood gutters in their unnervingly large collection of ceremonial knives.
There are plenty of theistic Satanists I know who are also great people.
The Church of Satan doesn’t believe in the devil. It doesn’t even recognise ‘Satan’ as a physical or spiritual being. As far as the Church is concerned, there is no such thing as heaven or hell.
And human sacrifice? Like, that kind of thing might happen in the Highest Orders of the Left-Hand Path, the Skull and Bones-type societies George W. Bush was a part of - so conspirators claim - like, I want to be expressly clear that suggesting Satanists make human sacrifices is akin to saying all Muslims are terrorists. Seriously. You're just discrediting a group of people who have enough troubles being recognized as valid to start.
I assure you, I have visited branches of the Church of Satan, and they are actually filled generally with very good people, whose philosophy is mostly that of self-love and not taking any bullshit, combined with the dogmatic practice of Ceremonial Magick.
It just wasn't my cup of tea. I have enjoyed more of what I've seen from Thelemic orders, which do not identify as Satanic.