Lol. 3 months ago when emotions were high and arcange, as you said backed down.

This is a reflection of some witness thoughts about people posting on both chains

No, it is not a reflection of anything but the stance of one person at the time, 3 months ago, Arcange.

Or this post from a curation community, where some witness downvoted (including @themarkymark) for no apparent reason, at least none that were publicly explained, but apparently, through some discord conversation, the reason given was that @project.hope is doing his curation project both here and on Steem.

I dunno. If its true apparently they dont want to support a project that runs on Steem as well or it could be what @enforcer48 said. Im not familiar with that community so i cant judge.
If you want a answer on why they do it ask them. Then we can discuss the morality of their reasoning.

there is probably a lot more examples

There really isnt because you did your best to find some and you were found lacking. If you had a "smoking gun" youd let us know.
What you need to understand is that anyone that supports Steem and Justin is either:

1. Ignorant on what happened which is fine.
2. A immoral piece of shit.

There is no in-between.
There are many whales, witnesses on HIVE i openly make fun of and dislike on a personal basis (marky is a dick, wolfie a coward, netuoso a leech, etc.) but there is no world in which i will ever pick Justin Sun, a sociopath, over them when i look at all the facts of what happened.
You want everyone to just FORGIVE those that supported Justin. There has been a lot of hurt that happened and a lot of money at play. None of us are saints and forgivness doesnt just happen.