This is not entirely accurate. In tantra for example, it is a traditional idea to prefer the use of a human femur bone or skull cap taken from a criminal or from someone who died a traumatic, accidental, or violent death (executions included) to make a kangling or kapala for ritual purposes. There may be other instances/traditions where this is also true-I don't know for sure, but my guess is probably "yes". Not saying I agree or disagree with this practice...Just saying is all. Granted, you did say human bones wouldn't be used like this under "normal" circumstances. That, however, depends on your definition of normal, I guess.
Other than that, I can appreciate your post and respect your opinion-but this is not generally the way I personally do things. If something calls out to me, I will take it and use it. If it doesn't, I won't. For me, each situation will be different. I guess, for me, the bottom line is "it depends".
Enjoyed reading your post though.
Oh I understand the use of human parts but those are normally more maligned or malcontent in purpose in my experience and knowledge. Sort of like the old stories of the Hand of Glory taken from a thief or killer and used as a candle in many of the earlier books about Satanism and Witchcraft. Not saying if the need or purpose arose I wouldn't use them but as a norm its not something people are normally going to do, especially in many western traditions. In Eastern traditions its been a bit different, some might compare the old thuggee cult to Kali as examples of the maligned influence. I suppose the notion of LHP ans RHP as coming out of India / Tibet would potentially also fall into usage of human remains that are typically outside normative western practices.
The Kapala stuff reminds me of the holy relic that is to be found in many Catholic churches as relics from some martyr or saint. Granted not quite the same usage but the semi enshrinement of human parts based upon goodness or evilness of the person. But then how many kapala's are actually human skull remains versus how many are actually molded material? In India / Tibet probably a number of ancient ones are, in the US and Europe probably more are molded copies than actual human remains. I suppose one might equate it to how many human shrunken heads are there compared to copies that are made to resemble them.
But thank you for reminding me of the Kapala's and tantric influences. Off topic but do you know if the Kapala is more aligned to Red or Black Tantric practices? Always heard red but that dealt more with sexual than physical in the sense of death, destruction and blood to my understanding.