Yes, but in a lot of ways, the laws of society are a sufficiently objective moral basis, since those are the rules we chose for ourselves. Undermining those is just bad in so many ways.
In some cases, yes. But in other cases they just represent the view of the vocal majority or those in power. Laws are official and objective, morals are relative. It's fine to base decisions on agreed upon laws. Appealing to morality is just using your own opinions
I'm aware that all morals are opinions and are dependent on an underlying subjective stance, and therefore the platforms should remain neutral in order to accommodate different stances. I'm arguing that in this case, since this is about stopping the dismantling of the structure of the laws themselves, it's a stance that it's ok for a platform to take since it's in some way the most fundamental common ground that we all need to share to function together.
So, at worst, delete the post, not ban the user (though I don't support that). In my view, the posts are inferred by some to incite destruction, but there are equal grounds to say that no explicit order was made in any post. Again, it's personal opinion.