We'd probably agree on this: people respond to incentives created by system design. One example that comes to mind is how London's Congestion Charge and how it has changed traffic behavior over the years depending on how the rules change.

There is nothing inherent about fast, large-scale, or user-friendly communication that forces spam, scams, or propaganda. Its just that those outcomes emerge when things like engagement, attention, or "reach" are rewarded without being aligned to quality, truth, or mutual cooperation.

This is a well-studied problem in economics, but also behavioral science and psychology: change the incentive and feedback structure, and behavior reliably changes.

Based on the studies I've read in and around this topic, I think harmful dynamics are not inevitable properties of communication, but really contingent on how each system rewards actions taken by participants. The solution is not slowness or barriers, but better incentive alignment and feedback loops.