I am enjoying all of the comments here. I was lucky enough to study traffic-as-density-waves in younger days, and I think the future will be very positive. For this particular argument, I think the common themes to solve are lack of infrastructure, and the resulting safety hazards from casual users:
The setbacks:
The infrastructure currently does not support the reality of the populous renting scooters (and bikes and mopeds).
City planning was not developed around the recent technological availability of motorized personal transportation.
Humans are irresponsible, and will leave scooters in disruptive locations.
Humans are reckless, and a large portion won't abide by the established traffic safety.
This "last-mile" transportation movement is a result of public transportation being a poor experience: slow-moving, dirty, congested, mismanaged.
Positive thoughts:
"last-mile" transportation is highly effective if it could be implemented properly.
Proper implementation would require responsible user behavior and infrastructure compatibility.
An anecdote: The company Scoot, at least in SF, gave access to moped-like vehicles for casual commute. Great idea. Give people the ability to personally navigate dense populations without vehicle ownership.
The problem: driving a personal motorized vehicle in dense large-vehicle traffic is a major responsibility. For instance, riding a motorcycle is extremely dangerous, and the vast majority of motorcycle riders take their safety incredibly seriously. They vehemently abide by traffic laws because small mistakes can lead to major physical consequences.
Scoot riders have unilaterally behaved like inexperienced idiots in traffic. Running lights, making last minute decisions, and ignoring speed of traffic sensibility The casual nature of that commute style leads people to behave like they are on bicycles, when they are riding around already-frustrated car and truck drivers.
The same me-first attitude was clearly visible when scooters were widely available. Even with city permits, people are still selfish.
Solutions:
There are conscious decisions to make city-wide improvements in efficient transportation. Mass transit combined with low-impact personal vehicles would be a utopia. But no large city was designed with that reality in mind, and the "disruptive" companies that make these technologies accessible, often with the "ask-for-forgiveness" mantra, are very disruptive to both the pedestrian reality and the detriment of too many cars.
Tl:dr, people are selfish and reckless, and even smart and available technologies will be abused unless infrastructure is designed to handle human habits.