Barter still exists. It is largely inefficient as we don't see things having equal value. Even in barter, often some intermediate that was a form of money emerged, such as a staple food that could be stored for a relative long term. In smaller communities, there was a bit of not seeking equal exchange because belonging to the community was more important, but that doesn't scale well to larger groups and can lead to some people being taken advantage of and thus leaving the community if that is an option.

Violence is problematic for self evident reasons. Cooperation I already touched on about the community involvement, with all the same problems.

It isn't that we can't imagine a world without money, but that we quickly see the problems with it given the scale of modern day life.

As for post scarcity, it really depends upon what is post scarcity. Money becomes meaningless for things that are not scarce, but some things remain scarce.