Both of those uses of a bicycle - operation on a sidewalk and riding against traffic on a one-way street - are a violation of NYC traffic law [1]. The operator is the one causing danger, not the bicycle.
[1] http://www.nyc.gov/html/dot/downloads/pdf/bicyclerules_engli...
NYC has widespread ignoring of many traffic laws, and that does not bother me. I am talking about, in the context of widespread violations, what does bother me: the electric bikes. You could accept that there is some validity in what I say without agreeing with me.
Given the choice, I would not be in favor of pedestrians and bikers being forced to follow all traffic laws. However, I would be in favor of electric bikes being forced to follow all traffic laws, especially the one that bans them! :)
EDIT: I just read your edit,
> I find electric bikes even more destabilizing and most objectionable, because they are faster and quieter, and I think because they are favored by a statistical sample that skews toward more selfish/self-interested.
This is a good summary of my thoughts about electrical bicycles as well.