First, I want to put myself into perspective:-
1) I am an avid Geni user.
2) The genealogy site that I refrain from becoming subscribed to is the "church" website. As a religious (at least try to be) and culturally aware Jew, I feel very uncomfortable in becoming a member of their site, and this means I do not have easy access to their resources unless the information is elsewhere. (I, though, tend to turn a blind eye if someone else finds family information for me from there ... maybe this is a principle I still need to work on <smile> .)
3) Although I don't remember having explicit contact with the poster here, it could quite easily be me, that responds the same way that he received response, although I try to be very careful if I make a change to the wider family tree, that there is a source for the information. I see nothing wrong with documenting on Geni our family who were killed in the holocaust, and also from extracting information that others have submitted on Pages of Testimony at Yad Vashem, etc. - and this documentation should be a further memorial.
Now, a couple of general words. Like it or not, many of us can trace our relationship to each other, sometimes through one or two marriages and sometimes also a divorce in between (then can say that the relationship is through the children of the divorced couple, if there were). So, if one uses Geni, one needs to understand that this might be the consequence. I agree that MyHeritage is better for private family trees with less collaboration, but there I do not appreciate the person who gave me a third great-grandparent on my ancestry, that is probably not mine, and I have no way to change this.
Wide traceable families is especially true for those of us who have Dutch ancestors (whether Sephardi or Ashkenazi) as their records go back quite a number of centuries, and Jews were pretty consistent with their family names (especially the sephardim, although I have also found anomalies in my ancestry).
Also, this is true for those of us who have family connections to any of the big Rabbinic families, whose trees are generally well documented (although plenty of holes also exist).
With respect to the "hocus pocus" stuff that is done by this church - I have no idea and it does not really concern me. They could also stand outside Bushey cemetery in London, UK, Har haMenuchot in Jerusalem, Israel or whatever other Jewish cemetery and do their hocus-pocus there - and no one could stop them. Many years ago there were anti-missionary demonstrations in Jerusalem near Har HaZaitim (Mount of Olives) because they received permission to open a college (with church inside I assume) at this place.
I hope, though, that they don't make a bid to dunk the Geni disks and hard drives in a mikva [=natural pool] - because this will void the warranty (to put it lightly) <Joke> - and might be cause to need to examine the halachic [=Jewish Law] issues with such a scenario.
Thinking about it, I could also stand outside one of the cemeteries and say the "mi sheberach" [= Prayer for the Departed] for "the souls of all those who are buried here", but I don't expect that I will be doing this. Or I could stand outside one of the hospitals and say the "mi sheberach" prayer for "all the ill people who are hospitalised here". In the former case, it is up to the family to decide whether they appreciate this, and in the latter case it is (in most cases) up to the person himself.